# orm/interfaces.py
# Copyright (C) 2005-2011 the SQLAlchemy authors and contributors <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""

Contains various base classes used throughout the ORM.

Defines the now deprecated ORM extension classes as well
as ORM internals.

Other than the deprecated extensions, this module and the
classes within should be considered mostly private.

"""

from itertools import chain

from sqlalchemy import exc as sa_exc
from sqlalchemy import util
from sqlalchemy.sql import operators
deque = __import__('collections').deque

mapperutil = util.importlater('sqlalchemy.orm', 'util')

collections = None

__all__ = (
    'AttributeExtension',
    'EXT_CONTINUE',
    'EXT_STOP',
    'ExtensionOption',
    'InstrumentationManager',
    'LoaderStrategy',
    'MapperExtension',
    'MapperOption',
    'MapperProperty',
    'PropComparator',
    'PropertyOption',
    'SessionExtension',
    'StrategizedOption',
    'StrategizedProperty',
    'build_path',
    )

EXT_CONTINUE = util.symbol('EXT_CONTINUE')
EXT_STOP = util.symbol('EXT_STOP')

ONETOMANY = util.symbol('ONETOMANY')
MANYTOONE = util.symbol('MANYTOONE')
MANYTOMANY = util.symbol('MANYTOMANY')

from deprecated_interfaces import AttributeExtension, SessionExtension, \
    MapperExtension


class MapperProperty(object):
    """Manage the relationship of a ``Mapper`` to a single class
    attribute, as well as that attribute as it appears on individual
    instances of the class, including attribute instrumentation,
    attribute access, loading behavior, and dependency calculations.
    
    The most common occurrences of :class:`.MapperProperty` are the
    mapped :class:`.Column`, which is represented in a mapping as 
    an instance of :class:`.ColumnProperty`,
    and a reference to another class produced by :func:`.relationship`,
    represented in the mapping as an instance of :class:`.RelationshipProperty`.
    
    """

    cascade = ()
    """The set of 'cascade' attribute names.

    This collection is checked before the 'cascade_iterator' method is called.

    """

    def setup(self, context, entity, path, reduced_path, adapter, **kwargs):
        """Called by Query for the purposes of constructing a SQL statement.

        Each MapperProperty associated with the target mapper processes the
        statement referenced by the query context, adding columns and/or
        criterion as appropriate.
        """

        pass

    def create_row_processor(self, context, path, reduced_path, 
                                            mapper, row, adapter):
        """Return a 3-tuple consisting of three row processing functions.

        """
        return None, None, None

    def cascade_iterator(self, type_, state, visited_instances=None,
                            halt_on=None):
        """Iterate through instances related to the given instance for
        a particular 'cascade', starting with this MapperProperty.

        Return an iterator3-tuples (instance, mapper, state).

        Note that the 'cascade' collection on this MapperProperty is
        checked first for the given type before cascade_iterator is called.

        See PropertyLoader for the related instance implementation.
        """

        return iter(())

    def set_parent(self, parent, init):
        self.parent = parent

    def instrument_class(self, mapper):
        raise NotImplementedError()

    _compile_started = False
    _compile_finished = False

    def init(self):
        """Called after all mappers are created to assemble
        relationships between mappers and perform other post-mapper-creation
        initialization steps.

        """
        self._compile_started = True
        self.do_init()
        self._compile_finished = True

    @property
    def class_attribute(self):
        """Return the class-bound descriptor corresponding to this
        MapperProperty."""

        return getattr(self.parent.class_, self.key)

    def do_init(self):
        """Perform subclass-specific initialization post-mapper-creation
        steps.

        This is a template method called by the ``MapperProperty``
        object's init() method.

        """

        pass

    def post_instrument_class(self, mapper):
        """Perform instrumentation adjustments that need to occur
        after init() has completed.

        """
        pass

    def per_property_preprocessors(self, uow):
        pass

    def is_primary(self):
        """Return True if this ``MapperProperty``'s mapper is the
        primary mapper for its class.

        This flag is used to indicate that the ``MapperProperty`` can
        define attribute instrumentation for the class at the class
        level (as opposed to the individual instance level).
        """

        return not self.parent.non_primary

    def merge(self, session, source_state, source_dict, dest_state,
                dest_dict, load, _recursive):
        """Merge the attribute represented by this ``MapperProperty``
        from source to destination object"""

        pass

    def compare(self, operator, value, **kw):
        """Return a compare operation for the columns represented by
        this ``MapperProperty`` to the given value, which may be a
        column value or an instance.  'operator' is an operator from
        the operators module, or from sql.Comparator.

        By default uses the PropComparator attached to this MapperProperty
        under the attribute name "comparator".
        """

        return operator(self.comparator, value)

class PropComparator(operators.ColumnOperators):
    """Defines comparison operations for MapperProperty objects.

    User-defined subclasses of :class:`.PropComparator` may be created. The
    built-in Python comparison and math operator methods, such as
    ``__eq__()``, ``__lt__()``, ``__add__()``, can be overridden to provide
    new operator behavior. The custom :class:`.PropComparator` is passed to
    the mapper property via the ``comparator_factory`` argument. In each case,
    the appropriate subclass of :class:`.PropComparator` should be used::

        from sqlalchemy.orm.properties import \\
                                ColumnProperty,\\
                                CompositeProperty,\\
                                RelationshipProperty

        class MyColumnComparator(ColumnProperty.Comparator):
            pass

        class MyCompositeComparator(CompositeProperty.Comparator):
            pass

        class MyRelationshipComparator(RelationshipProperty.Comparator):
            pass

    """

    def __init__(self, prop, mapper, adapter=None):
        self.prop = self.property = prop
        self.mapper = mapper
        self.adapter = adapter

    def __clause_element__(self):
        raise NotImplementedError("%r" % self)

    def adapted(self, adapter):
        """Return a copy of this PropComparator which will use the given
        adaption function on the local side of generated expressions.

        """

        return self.__class__(self.prop, self.mapper, adapter)

    @staticmethod
    def any_op(a, b, **kwargs):
        return a.any(b, **kwargs)

    @staticmethod
    def has_op(a, b, **kwargs):
        return a.has(b, **kwargs)

    @staticmethod
    def of_type_op(a, class_):
        return a.of_type(class_)

    def of_type(self, class_):
        """Redefine this object in terms of a polymorphic subclass.

        Returns a new PropComparator from which further criterion can be
        evaluated.

        e.g.::

            query.join(Company.employees.of_type(Engineer)).\\
               filter(Engineer.name=='foo')

        :param \class_: a class or mapper indicating that criterion will be against
            this specific subclass.


        """

        return self.operate(PropComparator.of_type_op, class_)

    def any(self, criterion=None, **kwargs):
        """Return true if this collection contains any member that meets the
        given criterion.

        The usual implementation of ``any()`` is 
        :meth:`.RelationshipProperty.Comparator.any`.

        :param criterion: an optional ClauseElement formulated against the 
          member class' table or attributes.

        :param \**kwargs: key/value pairs corresponding to member class attribute 
          names which will be compared via equality to the corresponding
          values.

        """

        return self.operate(PropComparator.any_op, criterion, **kwargs)

    def has(self, criterion=None, **kwargs):
        """Return true if this element references a member which meets the
        given criterion.

        The usual implementation of ``has()`` is 
        :meth:`.RelationshipProperty.Comparator.has`.

        :param criterion: an optional ClauseElement formulated against the 
          member class' table or attributes.

        :param \**kwargs: key/value pairs corresponding to member class attribute 
          names which will be compared via equality to the corresponding
          values.

        """

        return self.operate(PropComparator.has_op, criterion, **kwargs)


class StrategizedProperty(MapperProperty):
    """A MapperProperty which uses selectable strategies to affect
    loading behavior.

    There is a single strategy selected by default.  Alternate
    strategies can be selected at Query time through the usage of
    ``StrategizedOption`` objects via the Query.options() method.

    """

    def _get_context_strategy(self, context, reduced_path):
        key = ('loaderstrategy', reduced_path)
        if key in context.attributes:
            cls = context.attributes[key]
            try:
                return self._strategies[cls]
            except KeyError:
                return self.__init_strategy(cls)
        else:
            return self.strategy

    def _get_strategy(self, cls):
        try:
            return self._strategies[cls]
        except KeyError:
            return self.__init_strategy(cls)

    def __init_strategy(self, cls):
        self._strategies[cls] = strategy = cls(self)
        return strategy

    def setup(self, context, entity, path, reduced_path, adapter, **kwargs):
        self._get_context_strategy(context, reduced_path + (self.key,)).\
                    setup_query(context, entity, path, 
                                    reduced_path, adapter, **kwargs)

    def create_row_processor(self, context, path, reduced_path, mapper, row, adapter):
        return self._get_context_strategy(context, reduced_path + (self.key,)).\
                    create_row_processor(context, path, 
                                    reduced_path, mapper, row, adapter)

    def do_init(self):
        self._strategies = {}
        self.strategy = self.__init_strategy(self.strategy_class)

    def post_instrument_class(self, mapper):
        if self.is_primary() and \
            not mapper.class_manager._attr_has_impl(self.key):
            self.strategy.init_class_attribute(mapper)

def build_path(entity, key, prev=None):
    if prev:
        return prev + (entity, key)
    else:
        return (entity, key)

def serialize_path(path):
    if path is None:
        return None

    return zip(
        [m.class_ for m in [path[i] for i in range(0, len(path), 2)]], 
        [path[i] for i in range(1, len(path), 2)] + [None]
    )

def deserialize_path(path):
    if path is None:
        return None

    p = tuple(chain(*[(mapperutil.class_mapper(cls), key) for cls, key in path]))
    if p and p[-1] is None:
        p = p[0:-1]
    return p

class MapperOption(object):
    """Describe a modification to a Query."""

    propagate_to_loaders = False
    """if True, indicate this option should be carried along 
    Query object generated by scalar or object lazy loaders.
    """

    def process_query(self, query):
        pass

    def process_query_conditionally(self, query):
        """same as process_query(), except that this option may not
        apply to the given query.

        Used when secondary loaders resend existing options to a new
        Query."""

        self.process_query(query)

class PropertyOption(MapperOption):
    """A MapperOption that is applied to a property off the mapper or
    one of its child mappers, identified by a dot-separated key
    or list of class-bound attributes. """

    def __init__(self, key, mapper=None):
        self.key = key
        self.mapper = mapper

    def process_query(self, query):
        self._process(query, True)

    def process_query_conditionally(self, query):
        self._process(query, False)

    def _process(self, query, raiseerr):
        paths, mappers = self._get_paths(query, raiseerr)
        if paths:
            self.process_query_property(query, paths, mappers)

    def process_query_property(self, query, paths, mappers):
        pass

    def __getstate__(self):
        d = self.__dict__.copy()
        d['key'] = ret = []
        for token in util.to_list(self.key):
            if isinstance(token, PropComparator):
                ret.append((token.mapper.class_, token.key))
            else:
                ret.append(token)
        return d

    def __setstate__(self, state):
        ret = []
        for key in state['key']:
            if isinstance(key, tuple):
                cls, propkey = key
                ret.append(getattr(cls, propkey))
            else:
                ret.append(key)
        state['key'] = tuple(ret)
        self.__dict__ = state

    def _find_entity_prop_comparator(self, query, token, mapper, raiseerr):
        if mapperutil._is_aliased_class(mapper):
            searchfor = mapper
            isa = False
        else:
            searchfor = mapperutil._class_to_mapper(mapper)
            isa = True
        for ent in query._mapper_entities:
            if searchfor is ent.path_entity or isa \
                and searchfor.common_parent(ent.path_entity):
                return ent
        else:
            if raiseerr:
                if not list(query._mapper_entities):
                    raise sa_exc.ArgumentError(
                        "Query has only expression-based entities - "
                        "can't find property named '%s'."
                         % (token, )
                    )
                else:
                    raise sa_exc.ArgumentError(
                        "Can't find property '%s' on any entity "
                        "specified in this Query.  Note the full path " 
                        "from root (%s) to target entity must be specified." 
                        % (token, ",".join(str(x) for 
                            x in query._mapper_entities))
                    )
            else:
                return None

    def _find_entity_basestring(self, query, token, raiseerr):
        for ent in query._mapper_entities:
            # return only the first _MapperEntity when searching
            # based on string prop name.   Ideally object
            # attributes are used to specify more exactly.
            return ent
        else:
            if raiseerr:
                raise sa_exc.ArgumentError(
                    "Query has only expression-based entities - "
                    "can't find property named '%s'."
                     % (token, )
                )
            else:
                return None

    def _get_paths(self, query, raiseerr):
        path = None
        entity = None
        l = []
        mappers = []

        # _current_path implies we're in a 
        # secondary load with an existing path
        current_path = list(query._current_path)

        tokens = deque(self.key)
        while tokens:
            token = tokens.popleft()
            if isinstance(token, basestring):
                sub_tokens = token.split(".", 1)
                token = sub_tokens[0]
                tokens.extendleft(sub_tokens[1:])

                # exhaust current_path before
                # matching tokens to entities
                if current_path:
                    if current_path[1] == token:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []

                if not entity:
                    entity = self._find_entity_basestring(
                                        query, 
                                        token, 
                                        raiseerr)
                    if entity is None:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(mapper)
                if hasattr(mapper.class_, token):
                    prop = getattr(mapper.class_, token).property
                else:
                    if raiseerr:
                        raise sa_exc.ArgumentError(
                            "Can't find property named '%s' on the "
                            "mapped entity %s in this Query. " % (
                                token, mapper)
                        )
                    else:
                        return [], []
            elif isinstance(token, PropComparator):
                prop = token.property

                # exhaust current_path before
                # matching tokens to entities
                if current_path:
                    if current_path[0:2] == \
                            [token.parententity, prop.key]:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []

                if not entity:
                    entity = self._find_entity_prop_comparator(
                                            query,
                                            prop.key, 
                                            token.parententity, 
                                            raiseerr)
                    if not entity:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(prop.parent)
            else:
                raise sa_exc.ArgumentError(
                        "mapper option expects "
                        "string key or list of attributes")
            assert prop is not None
            path = build_path(path_element, prop.key, path)
            l.append(path)
            if getattr(token, '_of_type', None):
                path_element = mapper = token._of_type
            else:
                path_element = mapper = getattr(prop, 'mapper', None)
                if mapper is None and tokens:
                    raise sa_exc.ArgumentError(
                        "Attribute '%s' of entity '%s' does not "
                        "refer to a mapped entity" %
                        (token, entity)
                    )
            if path_element:
                path_element = path_element

        if current_path:
            # ran out of tokens before 
            # current_path was exhausted.
            assert not tokens
            return [], []

        return l, mappers

class StrategizedOption(PropertyOption):
    """A MapperOption that affects which LoaderStrategy will be used
    for an operation by a StrategizedProperty.
    """

    chained = False

    def process_query_property(self, query, paths, mappers):

        # _get_context_strategy may receive the path in terms of a base
        # mapper - e.g.  options(eagerload_all(Company.employees,
        # Engineer.machines)) in the polymorphic tests leads to
        # "(Person, 'machines')" in the path due to the mechanics of how
        # the eager strategy builds up the path

        if self.chained:
            for path in paths:
                query._attributes[('loaderstrategy',
                                  _reduce_path(path))] = \
                    self.get_strategy_class()
        else:
            query._attributes[('loaderstrategy',
                              _reduce_path(paths[-1]))] = \
                self.get_strategy_class()

    def get_strategy_class(self):
        raise NotImplementedError()

def _reduce_path(path):
    """Convert a (mapper, path) path to use base mappers.

    This is used to allow more open ended selection of loader strategies, i.e.
    Mapper -> prop1 -> Subclass -> prop2, where Subclass is a sub-mapper
    of the mapper referenced by Mapper.prop1.

    """
    return tuple([i % 2 != 0 and 
                    element or 
                    getattr(element, 'base_mapper', element) 
                    for i, element in enumerate(path)])

class LoaderStrategy(object):
    """Describe the loading behavior of a StrategizedProperty object.

    The ``LoaderStrategy`` interacts with the querying process in three
    ways:

    * it controls the configuration of the ``InstrumentedAttribute``
      placed on a class to handle the behavior of the attribute.  this
      may involve setting up class-level callable functions to fire
      off a select operation when the attribute is first accessed
      (i.e. a lazy load)

    * it processes the ``QueryContext`` at statement construction time,
      where it can modify the SQL statement that is being produced.
      Simple column attributes may add their represented column to the
      list of selected columns, *eager loading* properties may add
      ``LEFT OUTER JOIN`` clauses to the statement.

    * It produces "row processor" functions at result fetching time.
      These "row processor" functions populate a particular attribute
      on a particular mapped instance.

    """
    def __init__(self, parent):
        self.parent_property = parent
        self.is_class_level = False
        self.parent = self.parent_property.parent
        self.key = self.parent_property.key
        # TODO: there's no particular reason we need
        # the separate .init() method at this point.
        # It's possible someone has written their
        # own LS object.
        self.init()

    def init(self):
        raise NotImplementedError("LoaderStrategy")

    def init_class_attribute(self, mapper):
        pass

    def setup_query(self, context, entity, path, reduced_path, adapter, **kwargs):
        pass

    def create_row_processor(self, context, path, reduced_path, mapper, 
                                row, adapter):
        """Return row processing functions which fulfill the contract
        specified by MapperProperty.create_row_processor.

        StrategizedProperty delegates its create_row_processor method
        directly to this method. """

        return None, None, None

    def __str__(self):
        return str(self.parent_property)

    def debug_callable(self, fn, logger, announcement, logfn):
        if announcement:
            logger.debug(announcement)
        if logfn:
            def call(*args, **kwargs):
                logger.debug(logfn(*args, **kwargs))
                return fn(*args, **kwargs)
            return call
        else:
            return fn

class InstrumentationManager(object):
    """User-defined class instrumentation extension.

    :class:`.InstrumentationManager` can be subclassed in order
    to change
    how class instrumentation proceeds. This class exists for
    the purposes of integration with other object management
    frameworks which would like to entirely modify the
    instrumentation methodology of the ORM, and is not intended
    for regular usage.  For interception of class instrumentation
    events, see :class:`.InstrumentationEvents`.

    For an example of :class:`.InstrumentationManager`, see the
    example :ref:`examples_instrumentation`.

    The API for this class should be considered as semi-stable,
    and may change slightly with new releases.

    """

    # r4361 added a mandatory (cls) constructor to this interface.
    # given that, perhaps class_ should be dropped from all of these
    # signatures.

    def __init__(self, class_):
        pass

    def manage(self, class_, manager):
        setattr(class_, '_default_class_manager', manager)

    def dispose(self, class_, manager):
        delattr(class_, '_default_class_manager')

    def manager_getter(self, class_):
        def get(cls):
            return cls._default_class_manager
        return get

    def instrument_attribute(self, class_, key, inst):
        pass

    def post_configure_attribute(self, class_, key, inst):
        pass

    def install_descriptor(self, class_, key, inst):
        setattr(class_, key, inst)

    def uninstall_descriptor(self, class_, key):
        delattr(class_, key)

    def install_member(self, class_, key, implementation):
        setattr(class_, key, implementation)

    def uninstall_member(self, class_, key):
        delattr(class_, key)

    def instrument_collection_class(self, class_, key, collection_class):
        global collections
        if collections is None:
            from sqlalchemy.orm import collections
        return collections.prepare_instrumentation(collection_class)

    def get_instance_dict(self, class_, instance):
        return instance.__dict__

    def initialize_instance_dict(self, class_, instance):
        pass

    def install_state(self, class_, instance, state):
        setattr(instance, '_default_state', state)

    def remove_state(self, class_, instance):
        delattr(instance, '_default_state')

    def state_getter(self, class_):
        return lambda instance: getattr(instance, '_default_state')

    def dict_getter(self, class_):
        return lambda inst: self.get_instance_dict(class_, inst)

0bb6865d8d653e4ef46b8709727611fa4947dcf7
<mask token>


class PropertyOption(MapperOption):
    <mask token>

    def __init__(self, key, mapper=None):
        self.key = key
        self.mapper = mapper

    def process_query(self, query):
        self._process(query, True)

    def process_query_conditionally(self, query):
        self._process(query, False)

    def _process(self, query, raiseerr):
        paths, mappers = self._get_paths(query, raiseerr)
        if paths:
            self.process_query_property(query, paths, mappers)

    def process_query_property(self, query, paths, mappers):
        pass

    def __getstate__(self):
        d = self.__dict__.copy()
        d['key'] = ret = []
        for token in util.to_list(self.key):
            if isinstance(token, PropComparator):
                ret.append((token.mapper.class_, token.key))
            else:
                ret.append(token)
        return d

    def __setstate__(self, state):
        ret = []
        for key in state['key']:
            if isinstance(key, tuple):
                cls, propkey = key
                ret.append(getattr(cls, propkey))
            else:
                ret.append(key)
        state['key'] = tuple(ret)
        self.__dict__ = state

    def _find_entity_prop_comparator(self, query, token, mapper, raiseerr):
        if mapperutil._is_aliased_class(mapper):
            searchfor = mapper
            isa = False
        else:
            searchfor = mapperutil._class_to_mapper(mapper)
            isa = True
        for ent in query._mapper_entities:
            if searchfor is ent.path_entity or isa and searchfor.common_parent(
                ent.path_entity):
                return ent
        else:
            if raiseerr:
                if not list(query._mapper_entities):
                    raise sa_exc.ArgumentError(
                        "Query has only expression-based entities - can't find property named '%s'."
                         % (token,))
                else:
                    raise sa_exc.ArgumentError(
                        "Can't find property '%s' on any entity specified in this Query.  Note the full path from root (%s) to target entity must be specified."
                         % (token, ','.join(str(x) for x in query.
                        _mapper_entities)))
            else:
                return None

    def _find_entity_basestring(self, query, token, raiseerr):
        for ent in query._mapper_entities:
            return ent
        else:
            if raiseerr:
                raise sa_exc.ArgumentError(
                    "Query has only expression-based entities - can't find property named '%s'."
                     % (token,))
            else:
                return None

    def _get_paths(self, query, raiseerr):
        path = None
        entity = None
        l = []
        mappers = []
        current_path = list(query._current_path)
        tokens = deque(self.key)
        while tokens:
            token = tokens.popleft()
            if isinstance(token, basestring):
                sub_tokens = token.split('.', 1)
                token = sub_tokens[0]
                tokens.extendleft(sub_tokens[1:])
                if current_path:
                    if current_path[1] == token:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []
                if not entity:
                    entity = self._find_entity_basestring(query, token,
                        raiseerr)
                    if entity is None:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(mapper)
                if hasattr(mapper.class_, token):
                    prop = getattr(mapper.class_, token).property
                elif raiseerr:
                    raise sa_exc.ArgumentError(
                        "Can't find property named '%s' on the mapped entity %s in this Query. "
                         % (token, mapper))
                else:
                    return [], []
            elif isinstance(token, PropComparator):
                prop = token.property
                if current_path:
                    if current_path[0:2] == [token.parententity, prop.key]:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []
                if not entity:
                    entity = self._find_entity_prop_comparator(query, prop.
                        key, token.parententity, raiseerr)
                    if not entity:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(prop.parent)
            else:
                raise sa_exc.ArgumentError(
                    'mapper option expects string key or list of attributes')
            assert prop is not None
            path = build_path(path_element, prop.key, path)
            l.append(path)
            if getattr(token, '_of_type', None):
                path_element = mapper = token._of_type
            else:
                path_element = mapper = getattr(prop, 'mapper', None)
                if mapper is None and tokens:
                    raise sa_exc.ArgumentError(
                        "Attribute '%s' of entity '%s' does not refer to a mapped entity"
                         % (token, entity))
            if path_element:
                path_element = path_element
        if current_path:
            assert not tokens
            return [], []
        return l, mappers


class StrategizedOption(PropertyOption):
    """A MapperOption that affects which LoaderStrategy will be used
    for an operation by a StrategizedProperty.
    """
    chained = False

    def process_query_property(self, query, paths, mappers):
        if self.chained:
            for path in paths:
                query._attributes['loaderstrategy', _reduce_path(path)
                    ] = self.get_strategy_class()
        else:
            query._attributes['loaderstrategy', _reduce_path(paths[-1])
                ] = self.get_strategy_class()

    def get_strategy_class(self):
        raise NotImplementedError()


<mask token>


class LoaderStrategy(object):
    """Describe the loading behavior of a StrategizedProperty object.

    The ``LoaderStrategy`` interacts with the querying process in three
    ways:

    * it controls the configuration of the ``InstrumentedAttribute``
      placed on a class to handle the behavior of the attribute.  this
      may involve setting up class-level callable functions to fire
      off a select operation when the attribute is first accessed
      (i.e. a lazy load)

    * it processes the ``QueryContext`` at statement construction time,
      where it can modify the SQL statement that is being produced.
      Simple column attributes may add their represented column to the
      list of selected columns, *eager loading* properties may add
      ``LEFT OUTER JOIN`` clauses to the statement.

    * It produces "row processor" functions at result fetching time.
      These "row processor" functions populate a particular attribute
      on a particular mapped instance.

    """

    def __init__(self, parent):
        self.parent_property = parent
        self.is_class_level = False
        self.parent = self.parent_property.parent
        self.key = self.parent_property.key
        self.init()

    def init(self):
        raise NotImplementedError('LoaderStrategy')

    def init_class_attribute(self, mapper):
        pass

    def setup_query(self, context, entity, path, reduced_path, adapter, **
        kwargs):
        pass

    def create_row_processor(self, context, path, reduced_path, mapper, row,
        adapter):
        """Return row processing functions which fulfill the contract
        specified by MapperProperty.create_row_processor.

        StrategizedProperty delegates its create_row_processor method
        directly to this method. """
        return None, None, None

    def __str__(self):
        return str(self.parent_property)

    def debug_callable(self, fn, logger, announcement, logfn):
        if announcement:
            logger.debug(announcement)
        if logfn:

            def call(*args, **kwargs):
                logger.debug(logfn(*args, **kwargs))
                return fn(*args, **kwargs)
            return call
        else:
            return fn


class InstrumentationManager(object):
    """User-defined class instrumentation extension.

    :class:`.InstrumentationManager` can be subclassed in order
    to change
    how class instrumentation proceeds. This class exists for
    the purposes of integration with other object management
    frameworks which would like to entirely modify the
    instrumentation methodology of the ORM, and is not intended
    for regular usage.  For interception of class instrumentation
    events, see :class:`.InstrumentationEvents`.

    For an example of :class:`.InstrumentationManager`, see the
    example :ref:`examples_instrumentation`.

    The API for this class should be considered as semi-stable,
    and may change slightly with new releases.

    """

    def __init__(self, class_):
        pass

    def manage(self, class_, manager):
        setattr(class_, '_default_class_manager', manager)

    def dispose(self, class_, manager):
        delattr(class_, '_default_class_manager')

    def manager_getter(self, class_):

        def get(cls):
            return cls._default_class_manager
        return get

    def instrument_attribute(self, class_, key, inst):
        pass

    def post_configure_attribute(self, class_, key, inst):
        pass

    def install_descriptor(self, class_, key, inst):
        setattr(class_, key, inst)

    def uninstall_descriptor(self, class_, key):
        delattr(class_, key)

    def install_member(self, class_, key, implementation):
        setattr(class_, key, implementation)

    def uninstall_member(self, class_, key):
        delattr(class_, key)

    def instrument_collection_class(self, class_, key, collection_class):
        global collections
        if collections is None:
            from sqlalchemy.orm import collections
        return collections.prepare_instrumentation(collection_class)

    def get_instance_dict(self, class_, instance):
        return instance.__dict__

    def initialize_instance_dict(self, class_, instance):
        pass

    def install_state(self, class_, instance, state):
        setattr(instance, '_default_state', state)

    def remove_state(self, class_, instance):
        delattr(instance, '_default_state')

    def state_getter(self, class_):
        return lambda instance: getattr(instance, '_default_state')

    def dict_getter(self, class_):
        return lambda inst: self.get_instance_dict(class_, inst)

<mask token>


class PropComparator(operators.ColumnOperators):
    <mask token>
    <mask token>
    <mask token>

    def adapted(self, adapter):
        """Return a copy of this PropComparator which will use the given
        adaption function on the local side of generated expressions.

        """
        return self.__class__(self.prop, self.mapper, adapter)
    <mask token>

    @staticmethod
    def has_op(a, b, **kwargs):
        return a.has(b, **kwargs)
    <mask token>

    def of_type(self, class_):
        """Redefine this object in terms of a polymorphic subclass.

        Returns a new PropComparator from which further criterion can be
        evaluated.

        e.g.::

            query.join(Company.employees.of_type(Engineer)).\\
               filter(Engineer.name=='foo')

        :param \\class_: a class or mapper indicating that criterion will be against
            this specific subclass.


        """
        return self.operate(PropComparator.of_type_op, class_)

    def any(self, criterion=None, **kwargs):
        """Return true if this collection contains any member that meets the
        given criterion.

        The usual implementation of ``any()`` is 
        :meth:`.RelationshipProperty.Comparator.any`.

        :param criterion: an optional ClauseElement formulated against the 
          member class' table or attributes.

        :param \\**kwargs: key/value pairs corresponding to member class attribute 
          names which will be compared via equality to the corresponding
          values.

        """
        return self.operate(PropComparator.any_op, criterion, **kwargs)
    <mask token>


class StrategizedProperty(MapperProperty):
    """A MapperProperty which uses selectable strategies to affect
    loading behavior.

    There is a single strategy selected by default.  Alternate
    strategies can be selected at Query time through the usage of
    ``StrategizedOption`` objects via the Query.options() method.

    """

    def _get_context_strategy(self, context, reduced_path):
        key = 'loaderstrategy', reduced_path
        if key in context.attributes:
            cls = context.attributes[key]
            try:
                return self._strategies[cls]
            except KeyError:
                return self.__init_strategy(cls)
        else:
            return self.strategy

    def _get_strategy(self, cls):
        try:
            return self._strategies[cls]
        except KeyError:
            return self.__init_strategy(cls)

    def __init_strategy(self, cls):
        self._strategies[cls] = strategy = cls(self)
        return strategy

    def setup(self, context, entity, path, reduced_path, adapter, **kwargs):
        self._get_context_strategy(context, reduced_path + (self.key,)
            ).setup_query(context, entity, path, reduced_path, adapter, **
            kwargs)

    def create_row_processor(self, context, path, reduced_path, mapper, row,
        adapter):
        return self._get_context_strategy(context, reduced_path + (self.key,)
            ).create_row_processor(context, path, reduced_path, mapper, row,
            adapter)

    def do_init(self):
        self._strategies = {}
        self.strategy = self.__init_strategy(self.strategy_class)

    def post_instrument_class(self, mapper):
        if self.is_primary() and not mapper.class_manager._attr_has_impl(self
            .key):
            self.strategy.init_class_attribute(mapper)


<mask token>


class MapperOption(object):
    """Describe a modification to a Query."""
    propagate_to_loaders = False
    """if True, indicate this option should be carried along 
    Query object generated by scalar or object lazy loaders.
    """

    def process_query(self, query):
        pass

    def process_query_conditionally(self, query):
        """same as process_query(), except that this option may not
        apply to the given query.

        Used when secondary loaders resend existing options to a new
        Query."""
        self.process_query(query)


class PropertyOption(MapperOption):
    """A MapperOption that is applied to a property off the mapper or
    one of its child mappers, identified by a dot-separated key
    or list of class-bound attributes. """

    def __init__(self, key, mapper=None):
        self.key = key
        self.mapper = mapper

    def process_query(self, query):
        self._process(query, True)

    def process_query_conditionally(self, query):
        self._process(query, False)

    def _process(self, query, raiseerr):
        paths, mappers = self._get_paths(query, raiseerr)
        if paths:
            self.process_query_property(query, paths, mappers)

    def process_query_property(self, query, paths, mappers):
        pass

    def __getstate__(self):
        d = self.__dict__.copy()
        d['key'] = ret = []
        for token in util.to_list(self.key):
            if isinstance(token, PropComparator):
                ret.append((token.mapper.class_, token.key))
            else:
                ret.append(token)
        return d

    def __setstate__(self, state):
        ret = []
        for key in state['key']:
            if isinstance(key, tuple):
                cls, propkey = key
                ret.append(getattr(cls, propkey))
            else:
                ret.append(key)
        state['key'] = tuple(ret)
        self.__dict__ = state

    def _find_entity_prop_comparator(self, query, token, mapper, raiseerr):
        if mapperutil._is_aliased_class(mapper):
            searchfor = mapper
            isa = False
        else:
            searchfor = mapperutil._class_to_mapper(mapper)
            isa = True
        for ent in query._mapper_entities:
            if searchfor is ent.path_entity or isa and searchfor.common_parent(
                ent.path_entity):
                return ent
        else:
            if raiseerr:
                if not list(query._mapper_entities):
                    raise sa_exc.ArgumentError(
                        "Query has only expression-based entities - can't find property named '%s'."
                         % (token,))
                else:
                    raise sa_exc.ArgumentError(
                        "Can't find property '%s' on any entity specified in this Query.  Note the full path from root (%s) to target entity must be specified."
                         % (token, ','.join(str(x) for x in query.
                        _mapper_entities)))
            else:
                return None

    def _find_entity_basestring(self, query, token, raiseerr):
        for ent in query._mapper_entities:
            return ent
        else:
            if raiseerr:
                raise sa_exc.ArgumentError(
                    "Query has only expression-based entities - can't find property named '%s'."
                     % (token,))
            else:
                return None

    def _get_paths(self, query, raiseerr):
        path = None
        entity = None
        l = []
        mappers = []
        current_path = list(query._current_path)
        tokens = deque(self.key)
        while tokens:
            token = tokens.popleft()
            if isinstance(token, basestring):
                sub_tokens = token.split('.', 1)
                token = sub_tokens[0]
                tokens.extendleft(sub_tokens[1:])
                if current_path:
                    if current_path[1] == token:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []
                if not entity:
                    entity = self._find_entity_basestring(query, token,
                        raiseerr)
                    if entity is None:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(mapper)
                if hasattr(mapper.class_, token):
                    prop = getattr(mapper.class_, token).property
                elif raiseerr:
                    raise sa_exc.ArgumentError(
                        "Can't find property named '%s' on the mapped entity %s in this Query. "
                         % (token, mapper))
                else:
                    return [], []
            elif isinstance(token, PropComparator):
                prop = token.property
                if current_path:
                    if current_path[0:2] == [token.parententity, prop.key]:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []
                if not entity:
                    entity = self._find_entity_prop_comparator(query, prop.
                        key, token.parententity, raiseerr)
                    if not entity:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(prop.parent)
            else:
                raise sa_exc.ArgumentError(
                    'mapper option expects string key or list of attributes')
            assert prop is not None
            path = build_path(path_element, prop.key, path)
            l.append(path)
            if getattr(token, '_of_type', None):
                path_element = mapper = token._of_type
            else:
                path_element = mapper = getattr(prop, 'mapper', None)
                if mapper is None and tokens:
                    raise sa_exc.ArgumentError(
                        "Attribute '%s' of entity '%s' does not refer to a mapped entity"
                         % (token, entity))
            if path_element:
                path_element = path_element
        if current_path:
            assert not tokens
            return [], []
        return l, mappers


class StrategizedOption(PropertyOption):
    """A MapperOption that affects which LoaderStrategy will be used
    for an operation by a StrategizedProperty.
    """
    chained = False

    def process_query_property(self, query, paths, mappers):
        if self.chained:
            for path in paths:
                query._attributes['loaderstrategy', _reduce_path(path)
                    ] = self.get_strategy_class()
        else:
            query._attributes['loaderstrategy', _reduce_path(paths[-1])
                ] = self.get_strategy_class()

    def get_strategy_class(self):
        raise NotImplementedError()


<mask token>


class LoaderStrategy(object):
    """Describe the loading behavior of a StrategizedProperty object.

    The ``LoaderStrategy`` interacts with the querying process in three
    ways:

    * it controls the configuration of the ``InstrumentedAttribute``
      placed on a class to handle the behavior of the attribute.  this
      may involve setting up class-level callable functions to fire
      off a select operation when the attribute is first accessed
      (i.e. a lazy load)

    * it processes the ``QueryContext`` at statement construction time,
      where it can modify the SQL statement that is being produced.
      Simple column attributes may add their represented column to the
      list of selected columns, *eager loading* properties may add
      ``LEFT OUTER JOIN`` clauses to the statement.

    * It produces "row processor" functions at result fetching time.
      These "row processor" functions populate a particular attribute
      on a particular mapped instance.

    """

    def __init__(self, parent):
        self.parent_property = parent
        self.is_class_level = False
        self.parent = self.parent_property.parent
        self.key = self.parent_property.key
        self.init()

    def init(self):
        raise NotImplementedError('LoaderStrategy')

    def init_class_attribute(self, mapper):
        pass

    def setup_query(self, context, entity, path, reduced_path, adapter, **
        kwargs):
        pass

    def create_row_processor(self, context, path, reduced_path, mapper, row,
        adapter):
        """Return row processing functions which fulfill the contract
        specified by MapperProperty.create_row_processor.

        StrategizedProperty delegates its create_row_processor method
        directly to this method. """
        return None, None, None

    def __str__(self):
        return str(self.parent_property)

    def debug_callable(self, fn, logger, announcement, logfn):
        if announcement:
            logger.debug(announcement)
        if logfn:

            def call(*args, **kwargs):
                logger.debug(logfn(*args, **kwargs))
                return fn(*args, **kwargs)
            return call
        else:
            return fn


class InstrumentationManager(object):
    """User-defined class instrumentation extension.

    :class:`.InstrumentationManager` can be subclassed in order
    to change
    how class instrumentation proceeds. This class exists for
    the purposes of integration with other object management
    frameworks which would like to entirely modify the
    instrumentation methodology of the ORM, and is not intended
    for regular usage.  For interception of class instrumentation
    events, see :class:`.InstrumentationEvents`.

    For an example of :class:`.InstrumentationManager`, see the
    example :ref:`examples_instrumentation`.

    The API for this class should be considered as semi-stable,
    and may change slightly with new releases.

    """

    def __init__(self, class_):
        pass

    def manage(self, class_, manager):
        setattr(class_, '_default_class_manager', manager)

    def dispose(self, class_, manager):
        delattr(class_, '_default_class_manager')

    def manager_getter(self, class_):

        def get(cls):
            return cls._default_class_manager
        return get

    def instrument_attribute(self, class_, key, inst):
        pass

    def post_configure_attribute(self, class_, key, inst):
        pass

    def install_descriptor(self, class_, key, inst):
        setattr(class_, key, inst)

    def uninstall_descriptor(self, class_, key):
        delattr(class_, key)

    def install_member(self, class_, key, implementation):
        setattr(class_, key, implementation)

    def uninstall_member(self, class_, key):
        delattr(class_, key)

    def instrument_collection_class(self, class_, key, collection_class):
        global collections
        if collections is None:
            from sqlalchemy.orm import collections
        return collections.prepare_instrumentation(collection_class)

    def get_instance_dict(self, class_, instance):
        return instance.__dict__

    def initialize_instance_dict(self, class_, instance):
        pass

    def install_state(self, class_, instance, state):
        setattr(instance, '_default_state', state)

    def remove_state(self, class_, instance):
        delattr(instance, '_default_state')

    def state_getter(self, class_):
        return lambda instance: getattr(instance, '_default_state')

    def dict_getter(self, class_):
        return lambda inst: self.get_instance_dict(class_, inst)

<mask token>


class MapperProperty(object):
    <mask token>
    <mask token>
    <mask token>
    <mask token>
    <mask token>

    def cascade_iterator(self, type_, state, visited_instances=None,
        halt_on=None):
        """Iterate through instances related to the given instance for
        a particular 'cascade', starting with this MapperProperty.

        Return an iterator3-tuples (instance, mapper, state).

        Note that the 'cascade' collection on this MapperProperty is
        checked first for the given type before cascade_iterator is called.

        See PropertyLoader for the related instance implementation.
        """
        return iter(())
    <mask token>

    def instrument_class(self, mapper):
        raise NotImplementedError()
    <mask token>
    <mask token>
    <mask token>
    <mask token>

    def do_init(self):
        """Perform subclass-specific initialization post-mapper-creation
        steps.

        This is a template method called by the ``MapperProperty``
        object's init() method.

        """
        pass
    <mask token>
    <mask token>

    def is_primary(self):
        """Return True if this ``MapperProperty``'s mapper is the
        primary mapper for its class.

        This flag is used to indicate that the ``MapperProperty`` can
        define attribute instrumentation for the class at the class
        level (as opposed to the individual instance level).
        """
        return not self.parent.non_primary

    def merge(self, session, source_state, source_dict, dest_state,
        dest_dict, load, _recursive):
        """Merge the attribute represented by this ``MapperProperty``
        from source to destination object"""
        pass
    <mask token>


class PropComparator(operators.ColumnOperators):
    """Defines comparison operations for MapperProperty objects.

    User-defined subclasses of :class:`.PropComparator` may be created. The
    built-in Python comparison and math operator methods, such as
    ``__eq__()``, ``__lt__()``, ``__add__()``, can be overridden to provide
    new operator behavior. The custom :class:`.PropComparator` is passed to
    the mapper property via the ``comparator_factory`` argument. In each case,
    the appropriate subclass of :class:`.PropComparator` should be used::

        from sqlalchemy.orm.properties import \\
                                ColumnProperty,\\
                                CompositeProperty,\\
                                RelationshipProperty

        class MyColumnComparator(ColumnProperty.Comparator):
            pass

        class MyCompositeComparator(CompositeProperty.Comparator):
            pass

        class MyRelationshipComparator(RelationshipProperty.Comparator):
            pass

    """

    def __init__(self, prop, mapper, adapter=None):
        self.prop = self.property = prop
        self.mapper = mapper
        self.adapter = adapter

    def __clause_element__(self):
        raise NotImplementedError('%r' % self)

    def adapted(self, adapter):
        """Return a copy of this PropComparator which will use the given
        adaption function on the local side of generated expressions.

        """
        return self.__class__(self.prop, self.mapper, adapter)

    @staticmethod
    def any_op(a, b, **kwargs):
        return a.any(b, **kwargs)

    @staticmethod
    def has_op(a, b, **kwargs):
        return a.has(b, **kwargs)

    @staticmethod
    def of_type_op(a, class_):
        return a.of_type(class_)

    def of_type(self, class_):
        """Redefine this object in terms of a polymorphic subclass.

        Returns a new PropComparator from which further criterion can be
        evaluated.

        e.g.::

            query.join(Company.employees.of_type(Engineer)).\\
               filter(Engineer.name=='foo')

        :param \\class_: a class or mapper indicating that criterion will be against
            this specific subclass.


        """
        return self.operate(PropComparator.of_type_op, class_)

    def any(self, criterion=None, **kwargs):
        """Return true if this collection contains any member that meets the
        given criterion.

        The usual implementation of ``any()`` is 
        :meth:`.RelationshipProperty.Comparator.any`.

        :param criterion: an optional ClauseElement formulated against the 
          member class' table or attributes.

        :param \\**kwargs: key/value pairs corresponding to member class attribute 
          names which will be compared via equality to the corresponding
          values.

        """
        return self.operate(PropComparator.any_op, criterion, **kwargs)

    def has(self, criterion=None, **kwargs):
        """Return true if this element references a member which meets the
        given criterion.

        The usual implementation of ``has()`` is 
        :meth:`.RelationshipProperty.Comparator.has`.

        :param criterion: an optional ClauseElement formulated against the 
          member class' table or attributes.

        :param \\**kwargs: key/value pairs corresponding to member class attribute 
          names which will be compared via equality to the corresponding
          values.

        """
        return self.operate(PropComparator.has_op, criterion, **kwargs)


class StrategizedProperty(MapperProperty):
    """A MapperProperty which uses selectable strategies to affect
    loading behavior.

    There is a single strategy selected by default.  Alternate
    strategies can be selected at Query time through the usage of
    ``StrategizedOption`` objects via the Query.options() method.

    """

    def _get_context_strategy(self, context, reduced_path):
        key = 'loaderstrategy', reduced_path
        if key in context.attributes:
            cls = context.attributes[key]
            try:
                return self._strategies[cls]
            except KeyError:
                return self.__init_strategy(cls)
        else:
            return self.strategy

    def _get_strategy(self, cls):
        try:
            return self._strategies[cls]
        except KeyError:
            return self.__init_strategy(cls)

    def __init_strategy(self, cls):
        self._strategies[cls] = strategy = cls(self)
        return strategy

    def setup(self, context, entity, path, reduced_path, adapter, **kwargs):
        self._get_context_strategy(context, reduced_path + (self.key,)
            ).setup_query(context, entity, path, reduced_path, adapter, **
            kwargs)

    def create_row_processor(self, context, path, reduced_path, mapper, row,
        adapter):
        return self._get_context_strategy(context, reduced_path + (self.key,)
            ).create_row_processor(context, path, reduced_path, mapper, row,
            adapter)

    def do_init(self):
        self._strategies = {}
        self.strategy = self.__init_strategy(self.strategy_class)

    def post_instrument_class(self, mapper):
        if self.is_primary() and not mapper.class_manager._attr_has_impl(self
            .key):
            self.strategy.init_class_attribute(mapper)


<mask token>


class MapperOption(object):
    """Describe a modification to a Query."""
    propagate_to_loaders = False
    """if True, indicate this option should be carried along 
    Query object generated by scalar or object lazy loaders.
    """

    def process_query(self, query):
        pass

    def process_query_conditionally(self, query):
        """same as process_query(), except that this option may not
        apply to the given query.

        Used when secondary loaders resend existing options to a new
        Query."""
        self.process_query(query)


class PropertyOption(MapperOption):
    """A MapperOption that is applied to a property off the mapper or
    one of its child mappers, identified by a dot-separated key
    or list of class-bound attributes. """

    def __init__(self, key, mapper=None):
        self.key = key
        self.mapper = mapper

    def process_query(self, query):
        self._process(query, True)

    def process_query_conditionally(self, query):
        self._process(query, False)

    def _process(self, query, raiseerr):
        paths, mappers = self._get_paths(query, raiseerr)
        if paths:
            self.process_query_property(query, paths, mappers)

    def process_query_property(self, query, paths, mappers):
        pass

    def __getstate__(self):
        d = self.__dict__.copy()
        d['key'] = ret = []
        for token in util.to_list(self.key):
            if isinstance(token, PropComparator):
                ret.append((token.mapper.class_, token.key))
            else:
                ret.append(token)
        return d

    def __setstate__(self, state):
        ret = []
        for key in state['key']:
            if isinstance(key, tuple):
                cls, propkey = key
                ret.append(getattr(cls, propkey))
            else:
                ret.append(key)
        state['key'] = tuple(ret)
        self.__dict__ = state

    def _find_entity_prop_comparator(self, query, token, mapper, raiseerr):
        if mapperutil._is_aliased_class(mapper):
            searchfor = mapper
            isa = False
        else:
            searchfor = mapperutil._class_to_mapper(mapper)
            isa = True
        for ent in query._mapper_entities:
            if searchfor is ent.path_entity or isa and searchfor.common_parent(
                ent.path_entity):
                return ent
        else:
            if raiseerr:
                if not list(query._mapper_entities):
                    raise sa_exc.ArgumentError(
                        "Query has only expression-based entities - can't find property named '%s'."
                         % (token,))
                else:
                    raise sa_exc.ArgumentError(
                        "Can't find property '%s' on any entity specified in this Query.  Note the full path from root (%s) to target entity must be specified."
                         % (token, ','.join(str(x) for x in query.
                        _mapper_entities)))
            else:
                return None

    def _find_entity_basestring(self, query, token, raiseerr):
        for ent in query._mapper_entities:
            return ent
        else:
            if raiseerr:
                raise sa_exc.ArgumentError(
                    "Query has only expression-based entities - can't find property named '%s'."
                     % (token,))
            else:
                return None

    def _get_paths(self, query, raiseerr):
        path = None
        entity = None
        l = []
        mappers = []
        current_path = list(query._current_path)
        tokens = deque(self.key)
        while tokens:
            token = tokens.popleft()
            if isinstance(token, basestring):
                sub_tokens = token.split('.', 1)
                token = sub_tokens[0]
                tokens.extendleft(sub_tokens[1:])
                if current_path:
                    if current_path[1] == token:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []
                if not entity:
                    entity = self._find_entity_basestring(query, token,
                        raiseerr)
                    if entity is None:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(mapper)
                if hasattr(mapper.class_, token):
                    prop = getattr(mapper.class_, token).property
                elif raiseerr:
                    raise sa_exc.ArgumentError(
                        "Can't find property named '%s' on the mapped entity %s in this Query. "
                         % (token, mapper))
                else:
                    return [], []
            elif isinstance(token, PropComparator):
                prop = token.property
                if current_path:
                    if current_path[0:2] == [token.parententity, prop.key]:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []
                if not entity:
                    entity = self._find_entity_prop_comparator(query, prop.
                        key, token.parententity, raiseerr)
                    if not entity:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(prop.parent)
            else:
                raise sa_exc.ArgumentError(
                    'mapper option expects string key or list of attributes')
            assert prop is not None
            path = build_path(path_element, prop.key, path)
            l.append(path)
            if getattr(token, '_of_type', None):
                path_element = mapper = token._of_type
            else:
                path_element = mapper = getattr(prop, 'mapper', None)
                if mapper is None and tokens:
                    raise sa_exc.ArgumentError(
                        "Attribute '%s' of entity '%s' does not refer to a mapped entity"
                         % (token, entity))
            if path_element:
                path_element = path_element
        if current_path:
            assert not tokens
            return [], []
        return l, mappers


class StrategizedOption(PropertyOption):
    """A MapperOption that affects which LoaderStrategy will be used
    for an operation by a StrategizedProperty.
    """
    chained = False

    def process_query_property(self, query, paths, mappers):
        if self.chained:
            for path in paths:
                query._attributes['loaderstrategy', _reduce_path(path)
                    ] = self.get_strategy_class()
        else:
            query._attributes['loaderstrategy', _reduce_path(paths[-1])
                ] = self.get_strategy_class()

    def get_strategy_class(self):
        raise NotImplementedError()


<mask token>


class LoaderStrategy(object):
    """Describe the loading behavior of a StrategizedProperty object.

    The ``LoaderStrategy`` interacts with the querying process in three
    ways:

    * it controls the configuration of the ``InstrumentedAttribute``
      placed on a class to handle the behavior of the attribute.  this
      may involve setting up class-level callable functions to fire
      off a select operation when the attribute is first accessed
      (i.e. a lazy load)

    * it processes the ``QueryContext`` at statement construction time,
      where it can modify the SQL statement that is being produced.
      Simple column attributes may add their represented column to the
      list of selected columns, *eager loading* properties may add
      ``LEFT OUTER JOIN`` clauses to the statement.

    * It produces "row processor" functions at result fetching time.
      These "row processor" functions populate a particular attribute
      on a particular mapped instance.

    """

    def __init__(self, parent):
        self.parent_property = parent
        self.is_class_level = False
        self.parent = self.parent_property.parent
        self.key = self.parent_property.key
        self.init()

    def init(self):
        raise NotImplementedError('LoaderStrategy')

    def init_class_attribute(self, mapper):
        pass

    def setup_query(self, context, entity, path, reduced_path, adapter, **
        kwargs):
        pass

    def create_row_processor(self, context, path, reduced_path, mapper, row,
        adapter):
        """Return row processing functions which fulfill the contract
        specified by MapperProperty.create_row_processor.

        StrategizedProperty delegates its create_row_processor method
        directly to this method. """
        return None, None, None

    def __str__(self):
        return str(self.parent_property)

    def debug_callable(self, fn, logger, announcement, logfn):
        if announcement:
            logger.debug(announcement)
        if logfn:

            def call(*args, **kwargs):
                logger.debug(logfn(*args, **kwargs))
                return fn(*args, **kwargs)
            return call
        else:
            return fn


class InstrumentationManager(object):
    """User-defined class instrumentation extension.

    :class:`.InstrumentationManager` can be subclassed in order
    to change
    how class instrumentation proceeds. This class exists for
    the purposes of integration with other object management
    frameworks which would like to entirely modify the
    instrumentation methodology of the ORM, and is not intended
    for regular usage.  For interception of class instrumentation
    events, see :class:`.InstrumentationEvents`.

    For an example of :class:`.InstrumentationManager`, see the
    example :ref:`examples_instrumentation`.

    The API for this class should be considered as semi-stable,
    and may change slightly with new releases.

    """

    def __init__(self, class_):
        pass

    def manage(self, class_, manager):
        setattr(class_, '_default_class_manager', manager)

    def dispose(self, class_, manager):
        delattr(class_, '_default_class_manager')

    def manager_getter(self, class_):

        def get(cls):
            return cls._default_class_manager
        return get

    def instrument_attribute(self, class_, key, inst):
        pass

    def post_configure_attribute(self, class_, key, inst):
        pass

    def install_descriptor(self, class_, key, inst):
        setattr(class_, key, inst)

    def uninstall_descriptor(self, class_, key):
        delattr(class_, key)

    def install_member(self, class_, key, implementation):
        setattr(class_, key, implementation)

    def uninstall_member(self, class_, key):
        delattr(class_, key)

    def instrument_collection_class(self, class_, key, collection_class):
        global collections
        if collections is None:
            from sqlalchemy.orm import collections
        return collections.prepare_instrumentation(collection_class)

    def get_instance_dict(self, class_, instance):
        return instance.__dict__

    def initialize_instance_dict(self, class_, instance):
        pass

    def install_state(self, class_, instance, state):
        setattr(instance, '_default_state', state)

    def remove_state(self, class_, instance):
        delattr(instance, '_default_state')

    def state_getter(self, class_):
        return lambda instance: getattr(instance, '_default_state')

    def dict_getter(self, class_):
        return lambda inst: self.get_instance_dict(class_, inst)

<mask token>


class MapperProperty(object):
    <mask token>
    <mask token>
    <mask token>

    def setup(self, context, entity, path, reduced_path, adapter, **kwargs):
        """Called by Query for the purposes of constructing a SQL statement.

        Each MapperProperty associated with the target mapper processes the
        statement referenced by the query context, adding columns and/or
        criterion as appropriate.
        """
        pass

    def create_row_processor(self, context, path, reduced_path, mapper, row,
        adapter):
        """Return a 3-tuple consisting of three row processing functions.

        """
        return None, None, None

    def cascade_iterator(self, type_, state, visited_instances=None,
        halt_on=None):
        """Iterate through instances related to the given instance for
        a particular 'cascade', starting with this MapperProperty.

        Return an iterator3-tuples (instance, mapper, state).

        Note that the 'cascade' collection on this MapperProperty is
        checked first for the given type before cascade_iterator is called.

        See PropertyLoader for the related instance implementation.
        """
        return iter(())

    def set_parent(self, parent, init):
        self.parent = parent

    def instrument_class(self, mapper):
        raise NotImplementedError()
    <mask token>
    <mask token>

    def init(self):
        """Called after all mappers are created to assemble
        relationships between mappers and perform other post-mapper-creation
        initialization steps.

        """
        self._compile_started = True
        self.do_init()
        self._compile_finished = True

    @property
    def class_attribute(self):
        """Return the class-bound descriptor corresponding to this
        MapperProperty."""
        return getattr(self.parent.class_, self.key)

    def do_init(self):
        """Perform subclass-specific initialization post-mapper-creation
        steps.

        This is a template method called by the ``MapperProperty``
        object's init() method.

        """
        pass

    def post_instrument_class(self, mapper):
        """Perform instrumentation adjustments that need to occur
        after init() has completed.

        """
        pass

    def per_property_preprocessors(self, uow):
        pass

    def is_primary(self):
        """Return True if this ``MapperProperty``'s mapper is the
        primary mapper for its class.

        This flag is used to indicate that the ``MapperProperty`` can
        define attribute instrumentation for the class at the class
        level (as opposed to the individual instance level).
        """
        return not self.parent.non_primary

    def merge(self, session, source_state, source_dict, dest_state,
        dest_dict, load, _recursive):
        """Merge the attribute represented by this ``MapperProperty``
        from source to destination object"""
        pass

    def compare(self, operator, value, **kw):
        """Return a compare operation for the columns represented by
        this ``MapperProperty`` to the given value, which may be a
        column value or an instance.  'operator' is an operator from
        the operators module, or from sql.Comparator.

        By default uses the PropComparator attached to this MapperProperty
        under the attribute name "comparator".
        """
        return operator(self.comparator, value)


class PropComparator(operators.ColumnOperators):
    """Defines comparison operations for MapperProperty objects.

    User-defined subclasses of :class:`.PropComparator` may be created. The
    built-in Python comparison and math operator methods, such as
    ``__eq__()``, ``__lt__()``, ``__add__()``, can be overridden to provide
    new operator behavior. The custom :class:`.PropComparator` is passed to
    the mapper property via the ``comparator_factory`` argument. In each case,
    the appropriate subclass of :class:`.PropComparator` should be used::

        from sqlalchemy.orm.properties import \\
                                ColumnProperty,\\
                                CompositeProperty,\\
                                RelationshipProperty

        class MyColumnComparator(ColumnProperty.Comparator):
            pass

        class MyCompositeComparator(CompositeProperty.Comparator):
            pass

        class MyRelationshipComparator(RelationshipProperty.Comparator):
            pass

    """

    def __init__(self, prop, mapper, adapter=None):
        self.prop = self.property = prop
        self.mapper = mapper
        self.adapter = adapter

    def __clause_element__(self):
        raise NotImplementedError('%r' % self)

    def adapted(self, adapter):
        """Return a copy of this PropComparator which will use the given
        adaption function on the local side of generated expressions.

        """
        return self.__class__(self.prop, self.mapper, adapter)

    @staticmethod
    def any_op(a, b, **kwargs):
        return a.any(b, **kwargs)

    @staticmethod
    def has_op(a, b, **kwargs):
        return a.has(b, **kwargs)

    @staticmethod
    def of_type_op(a, class_):
        return a.of_type(class_)

    def of_type(self, class_):
        """Redefine this object in terms of a polymorphic subclass.

        Returns a new PropComparator from which further criterion can be
        evaluated.

        e.g.::

            query.join(Company.employees.of_type(Engineer)).\\
               filter(Engineer.name=='foo')

        :param \\class_: a class or mapper indicating that criterion will be against
            this specific subclass.


        """
        return self.operate(PropComparator.of_type_op, class_)

    def any(self, criterion=None, **kwargs):
        """Return true if this collection contains any member that meets the
        given criterion.

        The usual implementation of ``any()`` is 
        :meth:`.RelationshipProperty.Comparator.any`.

        :param criterion: an optional ClauseElement formulated against the 
          member class' table or attributes.

        :param \\**kwargs: key/value pairs corresponding to member class attribute 
          names which will be compared via equality to the corresponding
          values.

        """
        return self.operate(PropComparator.any_op, criterion, **kwargs)

    def has(self, criterion=None, **kwargs):
        """Return true if this element references a member which meets the
        given criterion.

        The usual implementation of ``has()`` is 
        :meth:`.RelationshipProperty.Comparator.has`.

        :param criterion: an optional ClauseElement formulated against the 
          member class' table or attributes.

        :param \\**kwargs: key/value pairs corresponding to member class attribute 
          names which will be compared via equality to the corresponding
          values.

        """
        return self.operate(PropComparator.has_op, criterion, **kwargs)


class StrategizedProperty(MapperProperty):
    """A MapperProperty which uses selectable strategies to affect
    loading behavior.

    There is a single strategy selected by default.  Alternate
    strategies can be selected at Query time through the usage of
    ``StrategizedOption`` objects via the Query.options() method.

    """

    def _get_context_strategy(self, context, reduced_path):
        key = 'loaderstrategy', reduced_path
        if key in context.attributes:
            cls = context.attributes[key]
            try:
                return self._strategies[cls]
            except KeyError:
                return self.__init_strategy(cls)
        else:
            return self.strategy

    def _get_strategy(self, cls):
        try:
            return self._strategies[cls]
        except KeyError:
            return self.__init_strategy(cls)

    def __init_strategy(self, cls):
        self._strategies[cls] = strategy = cls(self)
        return strategy

    def setup(self, context, entity, path, reduced_path, adapter, **kwargs):
        self._get_context_strategy(context, reduced_path + (self.key,)
            ).setup_query(context, entity, path, reduced_path, adapter, **
            kwargs)

    def create_row_processor(self, context, path, reduced_path, mapper, row,
        adapter):
        return self._get_context_strategy(context, reduced_path + (self.key,)
            ).create_row_processor(context, path, reduced_path, mapper, row,
            adapter)

    def do_init(self):
        self._strategies = {}
        self.strategy = self.__init_strategy(self.strategy_class)

    def post_instrument_class(self, mapper):
        if self.is_primary() and not mapper.class_manager._attr_has_impl(self
            .key):
            self.strategy.init_class_attribute(mapper)


<mask token>


class MapperOption(object):
    """Describe a modification to a Query."""
    propagate_to_loaders = False
    """if True, indicate this option should be carried along 
    Query object generated by scalar or object lazy loaders.
    """

    def process_query(self, query):
        pass

    def process_query_conditionally(self, query):
        """same as process_query(), except that this option may not
        apply to the given query.

        Used when secondary loaders resend existing options to a new
        Query."""
        self.process_query(query)


class PropertyOption(MapperOption):
    """A MapperOption that is applied to a property off the mapper or
    one of its child mappers, identified by a dot-separated key
    or list of class-bound attributes. """

    def __init__(self, key, mapper=None):
        self.key = key
        self.mapper = mapper

    def process_query(self, query):
        self._process(query, True)

    def process_query_conditionally(self, query):
        self._process(query, False)

    def _process(self, query, raiseerr):
        paths, mappers = self._get_paths(query, raiseerr)
        if paths:
            self.process_query_property(query, paths, mappers)

    def process_query_property(self, query, paths, mappers):
        pass

    def __getstate__(self):
        d = self.__dict__.copy()
        d['key'] = ret = []
        for token in util.to_list(self.key):
            if isinstance(token, PropComparator):
                ret.append((token.mapper.class_, token.key))
            else:
                ret.append(token)
        return d

    def __setstate__(self, state):
        ret = []
        for key in state['key']:
            if isinstance(key, tuple):
                cls, propkey = key
                ret.append(getattr(cls, propkey))
            else:
                ret.append(key)
        state['key'] = tuple(ret)
        self.__dict__ = state

    def _find_entity_prop_comparator(self, query, token, mapper, raiseerr):
        if mapperutil._is_aliased_class(mapper):
            searchfor = mapper
            isa = False
        else:
            searchfor = mapperutil._class_to_mapper(mapper)
            isa = True
        for ent in query._mapper_entities:
            if searchfor is ent.path_entity or isa and searchfor.common_parent(
                ent.path_entity):
                return ent
        else:
            if raiseerr:
                if not list(query._mapper_entities):
                    raise sa_exc.ArgumentError(
                        "Query has only expression-based entities - can't find property named '%s'."
                         % (token,))
                else:
                    raise sa_exc.ArgumentError(
                        "Can't find property '%s' on any entity specified in this Query.  Note the full path from root (%s) to target entity must be specified."
                         % (token, ','.join(str(x) for x in query.
                        _mapper_entities)))
            else:
                return None

    def _find_entity_basestring(self, query, token, raiseerr):
        for ent in query._mapper_entities:
            return ent
        else:
            if raiseerr:
                raise sa_exc.ArgumentError(
                    "Query has only expression-based entities - can't find property named '%s'."
                     % (token,))
            else:
                return None

    def _get_paths(self, query, raiseerr):
        path = None
        entity = None
        l = []
        mappers = []
        current_path = list(query._current_path)
        tokens = deque(self.key)
        while tokens:
            token = tokens.popleft()
            if isinstance(token, basestring):
                sub_tokens = token.split('.', 1)
                token = sub_tokens[0]
                tokens.extendleft(sub_tokens[1:])
                if current_path:
                    if current_path[1] == token:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []
                if not entity:
                    entity = self._find_entity_basestring(query, token,
                        raiseerr)
                    if entity is None:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(mapper)
                if hasattr(mapper.class_, token):
                    prop = getattr(mapper.class_, token).property
                elif raiseerr:
                    raise sa_exc.ArgumentError(
                        "Can't find property named '%s' on the mapped entity %s in this Query. "
                         % (token, mapper))
                else:
                    return [], []
            elif isinstance(token, PropComparator):
                prop = token.property
                if current_path:
                    if current_path[0:2] == [token.parententity, prop.key]:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []
                if not entity:
                    entity = self._find_entity_prop_comparator(query, prop.
                        key, token.parententity, raiseerr)
                    if not entity:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(prop.parent)
            else:
                raise sa_exc.ArgumentError(
                    'mapper option expects string key or list of attributes')
            assert prop is not None
            path = build_path(path_element, prop.key, path)
            l.append(path)
            if getattr(token, '_of_type', None):
                path_element = mapper = token._of_type
            else:
                path_element = mapper = getattr(prop, 'mapper', None)
                if mapper is None and tokens:
                    raise sa_exc.ArgumentError(
                        "Attribute '%s' of entity '%s' does not refer to a mapped entity"
                         % (token, entity))
            if path_element:
                path_element = path_element
        if current_path:
            assert not tokens
            return [], []
        return l, mappers


class StrategizedOption(PropertyOption):
    """A MapperOption that affects which LoaderStrategy will be used
    for an operation by a StrategizedProperty.
    """
    chained = False

    def process_query_property(self, query, paths, mappers):
        if self.chained:
            for path in paths:
                query._attributes['loaderstrategy', _reduce_path(path)
                    ] = self.get_strategy_class()
        else:
            query._attributes['loaderstrategy', _reduce_path(paths[-1])
                ] = self.get_strategy_class()

    def get_strategy_class(self):
        raise NotImplementedError()


<mask token>


class LoaderStrategy(object):
    """Describe the loading behavior of a StrategizedProperty object.

    The ``LoaderStrategy`` interacts with the querying process in three
    ways:

    * it controls the configuration of the ``InstrumentedAttribute``
      placed on a class to handle the behavior of the attribute.  this
      may involve setting up class-level callable functions to fire
      off a select operation when the attribute is first accessed
      (i.e. a lazy load)

    * it processes the ``QueryContext`` at statement construction time,
      where it can modify the SQL statement that is being produced.
      Simple column attributes may add their represented column to the
      list of selected columns, *eager loading* properties may add
      ``LEFT OUTER JOIN`` clauses to the statement.

    * It produces "row processor" functions at result fetching time.
      These "row processor" functions populate a particular attribute
      on a particular mapped instance.

    """

    def __init__(self, parent):
        self.parent_property = parent
        self.is_class_level = False
        self.parent = self.parent_property.parent
        self.key = self.parent_property.key
        self.init()

    def init(self):
        raise NotImplementedError('LoaderStrategy')

    def init_class_attribute(self, mapper):
        pass

    def setup_query(self, context, entity, path, reduced_path, adapter, **
        kwargs):
        pass

    def create_row_processor(self, context, path, reduced_path, mapper, row,
        adapter):
        """Return row processing functions which fulfill the contract
        specified by MapperProperty.create_row_processor.

        StrategizedProperty delegates its create_row_processor method
        directly to this method. """
        return None, None, None

    def __str__(self):
        return str(self.parent_property)

    def debug_callable(self, fn, logger, announcement, logfn):
        if announcement:
            logger.debug(announcement)
        if logfn:

            def call(*args, **kwargs):
                logger.debug(logfn(*args, **kwargs))
                return fn(*args, **kwargs)
            return call
        else:
            return fn


class InstrumentationManager(object):
    """User-defined class instrumentation extension.

    :class:`.InstrumentationManager` can be subclassed in order
    to change
    how class instrumentation proceeds. This class exists for
    the purposes of integration with other object management
    frameworks which would like to entirely modify the
    instrumentation methodology of the ORM, and is not intended
    for regular usage.  For interception of class instrumentation
    events, see :class:`.InstrumentationEvents`.

    For an example of :class:`.InstrumentationManager`, see the
    example :ref:`examples_instrumentation`.

    The API for this class should be considered as semi-stable,
    and may change slightly with new releases.

    """

    def __init__(self, class_):
        pass

    def manage(self, class_, manager):
        setattr(class_, '_default_class_manager', manager)

    def dispose(self, class_, manager):
        delattr(class_, '_default_class_manager')

    def manager_getter(self, class_):

        def get(cls):
            return cls._default_class_manager
        return get

    def instrument_attribute(self, class_, key, inst):
        pass

    def post_configure_attribute(self, class_, key, inst):
        pass

    def install_descriptor(self, class_, key, inst):
        setattr(class_, key, inst)

    def uninstall_descriptor(self, class_, key):
        delattr(class_, key)

    def install_member(self, class_, key, implementation):
        setattr(class_, key, implementation)

    def uninstall_member(self, class_, key):
        delattr(class_, key)

    def instrument_collection_class(self, class_, key, collection_class):
        global collections
        if collections is None:
            from sqlalchemy.orm import collections
        return collections.prepare_instrumentation(collection_class)

    def get_instance_dict(self, class_, instance):
        return instance.__dict__

    def initialize_instance_dict(self, class_, instance):
        pass

    def install_state(self, class_, instance, state):
        setattr(instance, '_default_state', state)

    def remove_state(self, class_, instance):
        delattr(instance, '_default_state')

    def state_getter(self, class_):
        return lambda instance: getattr(instance, '_default_state')

    def dict_getter(self, class_):
        return lambda inst: self.get_instance_dict(class_, inst)

# orm/interfaces.py
# Copyright (C) 2005-2011 the SQLAlchemy authors and contributors <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""

Contains various base classes used throughout the ORM.

Defines the now deprecated ORM extension classes as well
as ORM internals.

Other than the deprecated extensions, this module and the
classes within should be considered mostly private.

"""

from itertools import chain

from sqlalchemy import exc as sa_exc
from sqlalchemy import util
from sqlalchemy.sql import operators
deque = __import__('collections').deque

mapperutil = util.importlater('sqlalchemy.orm', 'util')

collections = None

__all__ = (
    'AttributeExtension',
    'EXT_CONTINUE',
    'EXT_STOP',
    'ExtensionOption',
    'InstrumentationManager',
    'LoaderStrategy',
    'MapperExtension',
    'MapperOption',
    'MapperProperty',
    'PropComparator',
    'PropertyOption',
    'SessionExtension',
    'StrategizedOption',
    'StrategizedProperty',
    'build_path',
    )

EXT_CONTINUE = util.symbol('EXT_CONTINUE')
EXT_STOP = util.symbol('EXT_STOP')

ONETOMANY = util.symbol('ONETOMANY')
MANYTOONE = util.symbol('MANYTOONE')
MANYTOMANY = util.symbol('MANYTOMANY')

from deprecated_interfaces import AttributeExtension, SessionExtension, \
    MapperExtension


class MapperProperty(object):
    """Manage the relationship of a ``Mapper`` to a single class
    attribute, as well as that attribute as it appears on individual
    instances of the class, including attribute instrumentation,
    attribute access, loading behavior, and dependency calculations.
    
    The most common occurrences of :class:`.MapperProperty` are the
    mapped :class:`.Column`, which is represented in a mapping as 
    an instance of :class:`.ColumnProperty`,
    and a reference to another class produced by :func:`.relationship`,
    represented in the mapping as an instance of :class:`.RelationshipProperty`.
    
    """

    cascade = ()
    """The set of 'cascade' attribute names.

    This collection is checked before the 'cascade_iterator' method is called.

    """

    def setup(self, context, entity, path, reduced_path, adapter, **kwargs):
        """Called by Query for the purposes of constructing a SQL statement.

        Each MapperProperty associated with the target mapper processes the
        statement referenced by the query context, adding columns and/or
        criterion as appropriate.
        """

        pass

    def create_row_processor(self, context, path, reduced_path, 
                                            mapper, row, adapter):
        """Return a 3-tuple consisting of three row processing functions.

        """
        return None, None, None

    def cascade_iterator(self, type_, state, visited_instances=None,
                            halt_on=None):
        """Iterate through instances related to the given instance for
        a particular 'cascade', starting with this MapperProperty.

        Return an iterator3-tuples (instance, mapper, state).

        Note that the 'cascade' collection on this MapperProperty is
        checked first for the given type before cascade_iterator is called.

        See PropertyLoader for the related instance implementation.
        """

        return iter(())

    def set_parent(self, parent, init):
        self.parent = parent

    def instrument_class(self, mapper):
        raise NotImplementedError()

    _compile_started = False
    _compile_finished = False

    def init(self):
        """Called after all mappers are created to assemble
        relationships between mappers and perform other post-mapper-creation
        initialization steps.

        """
        self._compile_started = True
        self.do_init()
        self._compile_finished = True

    @property
    def class_attribute(self):
        """Return the class-bound descriptor corresponding to this
        MapperProperty."""

        return getattr(self.parent.class_, self.key)

    def do_init(self):
        """Perform subclass-specific initialization post-mapper-creation
        steps.

        This is a template method called by the ``MapperProperty``
        object's init() method.

        """

        pass

    def post_instrument_class(self, mapper):
        """Perform instrumentation adjustments that need to occur
        after init() has completed.

        """
        pass

    def per_property_preprocessors(self, uow):
        pass

    def is_primary(self):
        """Return True if this ``MapperProperty``'s mapper is the
        primary mapper for its class.

        This flag is used to indicate that the ``MapperProperty`` can
        define attribute instrumentation for the class at the class
        level (as opposed to the individual instance level).
        """

        return not self.parent.non_primary

    def merge(self, session, source_state, source_dict, dest_state,
                dest_dict, load, _recursive):
        """Merge the attribute represented by this ``MapperProperty``
        from source to destination object"""

        pass

    def compare(self, operator, value, **kw):
        """Return a compare operation for the columns represented by
        this ``MapperProperty`` to the given value, which may be a
        column value or an instance.  'operator' is an operator from
        the operators module, or from sql.Comparator.

        By default uses the PropComparator attached to this MapperProperty
        under the attribute name "comparator".
        """

        return operator(self.comparator, value)

class PropComparator(operators.ColumnOperators):
    """Defines comparison operations for MapperProperty objects.

    User-defined subclasses of :class:`.PropComparator` may be created. The
    built-in Python comparison and math operator methods, such as
    ``__eq__()``, ``__lt__()``, ``__add__()``, can be overridden to provide
    new operator behavior. The custom :class:`.PropComparator` is passed to
    the mapper property via the ``comparator_factory`` argument. In each case,
    the appropriate subclass of :class:`.PropComparator` should be used::

        from sqlalchemy.orm.properties import \\
                                ColumnProperty,\\
                                CompositeProperty,\\
                                RelationshipProperty

        class MyColumnComparator(ColumnProperty.Comparator):
            pass

        class MyCompositeComparator(CompositeProperty.Comparator):
            pass

        class MyRelationshipComparator(RelationshipProperty.Comparator):
            pass

    """

    def __init__(self, prop, mapper, adapter=None):
        self.prop = self.property = prop
        self.mapper = mapper
        self.adapter = adapter

    def __clause_element__(self):
        raise NotImplementedError("%r" % self)

    def adapted(self, adapter):
        """Return a copy of this PropComparator which will use the given
        adaption function on the local side of generated expressions.

        """

        return self.__class__(self.prop, self.mapper, adapter)

    @staticmethod
    def any_op(a, b, **kwargs):
        return a.any(b, **kwargs)

    @staticmethod
    def has_op(a, b, **kwargs):
        return a.has(b, **kwargs)

    @staticmethod
    def of_type_op(a, class_):
        return a.of_type(class_)

    def of_type(self, class_):
        """Redefine this object in terms of a polymorphic subclass.

        Returns a new PropComparator from which further criterion can be
        evaluated.

        e.g.::

            query.join(Company.employees.of_type(Engineer)).\\
               filter(Engineer.name=='foo')

        :param \class_: a class or mapper indicating that criterion will be against
            this specific subclass.


        """

        return self.operate(PropComparator.of_type_op, class_)

    def any(self, criterion=None, **kwargs):
        """Return true if this collection contains any member that meets the
        given criterion.

        The usual implementation of ``any()`` is 
        :meth:`.RelationshipProperty.Comparator.any`.

        :param criterion: an optional ClauseElement formulated against the 
          member class' table or attributes.

        :param \**kwargs: key/value pairs corresponding to member class attribute 
          names which will be compared via equality to the corresponding
          values.

        """

        return self.operate(PropComparator.any_op, criterion, **kwargs)

    def has(self, criterion=None, **kwargs):
        """Return true if this element references a member which meets the
        given criterion.

        The usual implementation of ``has()`` is 
        :meth:`.RelationshipProperty.Comparator.has`.

        :param criterion: an optional ClauseElement formulated against the 
          member class' table or attributes.

        :param \**kwargs: key/value pairs corresponding to member class attribute 
          names which will be compared via equality to the corresponding
          values.

        """

        return self.operate(PropComparator.has_op, criterion, **kwargs)


class StrategizedProperty(MapperProperty):
    """A MapperProperty which uses selectable strategies to affect
    loading behavior.

    There is a single strategy selected by default.  Alternate
    strategies can be selected at Query time through the usage of
    ``StrategizedOption`` objects via the Query.options() method.

    """

    def _get_context_strategy(self, context, reduced_path):
        key = ('loaderstrategy', reduced_path)
        if key in context.attributes:
            cls = context.attributes[key]
            try:
                return self._strategies[cls]
            except KeyError:
                return self.__init_strategy(cls)
        else:
            return self.strategy

    def _get_strategy(self, cls):
        try:
            return self._strategies[cls]
        except KeyError:
            return self.__init_strategy(cls)

    def __init_strategy(self, cls):
        self._strategies[cls] = strategy = cls(self)
        return strategy

    def setup(self, context, entity, path, reduced_path, adapter, **kwargs):
        self._get_context_strategy(context, reduced_path + (self.key,)).\
                    setup_query(context, entity, path, 
                                    reduced_path, adapter, **kwargs)

    def create_row_processor(self, context, path, reduced_path, mapper, row, adapter):
        return self._get_context_strategy(context, reduced_path + (self.key,)).\
                    create_row_processor(context, path, 
                                    reduced_path, mapper, row, adapter)

    def do_init(self):
        self._strategies = {}
        self.strategy = self.__init_strategy(self.strategy_class)

    def post_instrument_class(self, mapper):
        if self.is_primary() and \
            not mapper.class_manager._attr_has_impl(self.key):
            self.strategy.init_class_attribute(mapper)

def build_path(entity, key, prev=None):
    if prev:
        return prev + (entity, key)
    else:
        return (entity, key)

def serialize_path(path):
    if path is None:
        return None

    return zip(
        [m.class_ for m in [path[i] for i in range(0, len(path), 2)]], 
        [path[i] for i in range(1, len(path), 2)] + [None]
    )

def deserialize_path(path):
    if path is None:
        return None

    p = tuple(chain(*[(mapperutil.class_mapper(cls), key) for cls, key in path]))
    if p and p[-1] is None:
        p = p[0:-1]
    return p

class MapperOption(object):
    """Describe a modification to a Query."""

    propagate_to_loaders = False
    """if True, indicate this option should be carried along 
    Query object generated by scalar or object lazy loaders.
    """

    def process_query(self, query):
        pass

    def process_query_conditionally(self, query):
        """same as process_query(), except that this option may not
        apply to the given query.

        Used when secondary loaders resend existing options to a new
        Query."""

        self.process_query(query)

class PropertyOption(MapperOption):
    """A MapperOption that is applied to a property off the mapper or
    one of its child mappers, identified by a dot-separated key
    or list of class-bound attributes. """

    def __init__(self, key, mapper=None):
        self.key = key
        self.mapper = mapper

    def process_query(self, query):
        self._process(query, True)

    def process_query_conditionally(self, query):
        self._process(query, False)

    def _process(self, query, raiseerr):
        paths, mappers = self._get_paths(query, raiseerr)
        if paths:
            self.process_query_property(query, paths, mappers)

    def process_query_property(self, query, paths, mappers):
        pass

    def __getstate__(self):
        d = self.__dict__.copy()
        d['key'] = ret = []
        for token in util.to_list(self.key):
            if isinstance(token, PropComparator):
                ret.append((token.mapper.class_, token.key))
            else:
                ret.append(token)
        return d

    def __setstate__(self, state):
        ret = []
        for key in state['key']:
            if isinstance(key, tuple):
                cls, propkey = key
                ret.append(getattr(cls, propkey))
            else:
                ret.append(key)
        state['key'] = tuple(ret)
        self.__dict__ = state

    def _find_entity_prop_comparator(self, query, token, mapper, raiseerr):
        if mapperutil._is_aliased_class(mapper):
            searchfor = mapper
            isa = False
        else:
            searchfor = mapperutil._class_to_mapper(mapper)
            isa = True
        for ent in query._mapper_entities:
            if searchfor is ent.path_entity or isa \
                and searchfor.common_parent(ent.path_entity):
                return ent
        else:
            if raiseerr:
                if not list(query._mapper_entities):
                    raise sa_exc.ArgumentError(
                        "Query has only expression-based entities - "
                        "can't find property named '%s'."
                         % (token, )
                    )
                else:
                    raise sa_exc.ArgumentError(
                        "Can't find property '%s' on any entity "
                        "specified in this Query.  Note the full path " 
                        "from root (%s) to target entity must be specified." 
                        % (token, ",".join(str(x) for 
                            x in query._mapper_entities))
                    )
            else:
                return None

    def _find_entity_basestring(self, query, token, raiseerr):
        for ent in query._mapper_entities:
            # return only the first _MapperEntity when searching
            # based on string prop name.   Ideally object
            # attributes are used to specify more exactly.
            return ent
        else:
            if raiseerr:
                raise sa_exc.ArgumentError(
                    "Query has only expression-based entities - "
                    "can't find property named '%s'."
                     % (token, )
                )
            else:
                return None

    def _get_paths(self, query, raiseerr):
        path = None
        entity = None
        l = []
        mappers = []

        # _current_path implies we're in a 
        # secondary load with an existing path
        current_path = list(query._current_path)

        tokens = deque(self.key)
        while tokens:
            token = tokens.popleft()
            if isinstance(token, basestring):
                sub_tokens = token.split(".", 1)
                token = sub_tokens[0]
                tokens.extendleft(sub_tokens[1:])

                # exhaust current_path before
                # matching tokens to entities
                if current_path:
                    if current_path[1] == token:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []

                if not entity:
                    entity = self._find_entity_basestring(
                                        query, 
                                        token, 
                                        raiseerr)
                    if entity is None:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(mapper)
                if hasattr(mapper.class_, token):
                    prop = getattr(mapper.class_, token).property
                else:
                    if raiseerr:
                        raise sa_exc.ArgumentError(
                            "Can't find property named '%s' on the "
                            "mapped entity %s in this Query. " % (
                                token, mapper)
                        )
                    else:
                        return [], []
            elif isinstance(token, PropComparator):
                prop = token.property

                # exhaust current_path before
                # matching tokens to entities
                if current_path:
                    if current_path[0:2] == \
                            [token.parententity, prop.key]:
                        current_path = current_path[2:]
                        continue
                    else:
                        return [], []

                if not entity:
                    entity = self._find_entity_prop_comparator(
                                            query,
                                            prop.key, 
                                            token.parententity, 
                                            raiseerr)
                    if not entity:
                        return [], []
                    path_element = entity.path_entity
                    mapper = entity.mapper
                mappers.append(prop.parent)
            else:
                raise sa_exc.ArgumentError(
                        "mapper option expects "
                        "string key or list of attributes")
            assert prop is not None
            path = build_path(path_element, prop.key, path)
            l.append(path)
            if getattr(token, '_of_type', None):
                path_element = mapper = token._of_type
            else:
                path_element = mapper = getattr(prop, 'mapper', None)
                if mapper is None and tokens:
                    raise sa_exc.ArgumentError(
                        "Attribute '%s' of entity '%s' does not "
                        "refer to a mapped entity" %
                        (token, entity)
                    )
            if path_element:
                path_element = path_element

        if current_path:
            # ran out of tokens before 
            # current_path was exhausted.
            assert not tokens
            return [], []

        return l, mappers

class StrategizedOption(PropertyOption):
    """A MapperOption that affects which LoaderStrategy will be used
    for an operation by a StrategizedProperty.
    """

    chained = False

    def process_query_property(self, query, paths, mappers):

        # _get_context_strategy may receive the path in terms of a base
        # mapper - e.g.  options(eagerload_all(Company.employees,
        # Engineer.machines)) in the polymorphic tests leads to
        # "(Person, 'machines')" in the path due to the mechanics of how
        # the eager strategy builds up the path

        if self.chained:
            for path in paths:
                query._attributes[('loaderstrategy',
                                  _reduce_path(path))] = \
                    self.get_strategy_class()
        else:
            query._attributes[('loaderstrategy',
                              _reduce_path(paths[-1]))] = \
                self.get_strategy_class()

    def get_strategy_class(self):
        raise NotImplementedError()

def _reduce_path(path):
    """Convert a (mapper, path) path to use base mappers.

    This is used to allow more open ended selection of loader strategies, i.e.
    Mapper -> prop1 -> Subclass -> prop2, where Subclass is a sub-mapper
    of the mapper referenced by Mapper.prop1.

    """
    return tuple([i % 2 != 0 and 
                    element or 
                    getattr(element, 'base_mapper', element) 
                    for i, element in enumerate(path)])

class LoaderStrategy(object):
    """Describe the loading behavior of a StrategizedProperty object.

    The ``LoaderStrategy`` interacts with the querying process in three
    ways:

    * it controls the configuration of the ``InstrumentedAttribute``
      placed on a class to handle the behavior of the attribute.  this
      may involve setting up class-level callable functions to fire
      off a select operation when the attribute is first accessed
      (i.e. a lazy load)

    * it processes the ``QueryContext`` at statement construction time,
      where it can modify the SQL statement that is being produced.
      Simple column attributes may add their represented column to the
      list of selected columns, *eager loading* properties may add
      ``LEFT OUTER JOIN`` clauses to the statement.

    * It produces "row processor" functions at result fetching time.
      These "row processor" functions populate a particular attribute
      on a particular mapped instance.

    """
    def __init__(self, parent):
        self.parent_property = parent
        self.is_class_level = False
        self.parent = self.parent_property.parent
        self.key = self.parent_property.key
        # TODO: there's no particular reason we need
        # the separate .init() method at this point.
        # It's possible someone has written their
        # own LS object.
        self.init()

    def init(self):
        raise NotImplementedError("LoaderStrategy")

    def init_class_attribute(self, mapper):
        pass

    def setup_query(self, context, entity, path, reduced_path, adapter, **kwargs):
        pass

    def create_row_processor(self, context, path, reduced_path, mapper, 
                                row, adapter):
        """Return row processing functions which fulfill the contract
        specified by MapperProperty.create_row_processor.

        StrategizedProperty delegates its create_row_processor method
        directly to this method. """

        return None, None, None

    def __str__(self):
        return str(self.parent_property)

    def debug_callable(self, fn, logger, announcement, logfn):
        if announcement:
            logger.debug(announcement)
        if logfn:
            def call(*args, **kwargs):
                logger.debug(logfn(*args, **kwargs))
                return fn(*args, **kwargs)
            return call
        else:
            return fn

class InstrumentationManager(object):
    """User-defined class instrumentation extension.

    :class:`.InstrumentationManager` can be subclassed in order
    to change
    how class instrumentation proceeds. This class exists for
    the purposes of integration with other object management
    frameworks which would like to entirely modify the
    instrumentation methodology of the ORM, and is not intended
    for regular usage.  For interception of class instrumentation
    events, see :class:`.InstrumentationEvents`.

    For an example of :class:`.InstrumentationManager`, see the
    example :ref:`examples_instrumentation`.

    The API for this class should be considered as semi-stable,
    and may change slightly with new releases.

    """

    # r4361 added a mandatory (cls) constructor to this interface.
    # given that, perhaps class_ should be dropped from all of these
    # signatures.

    def __init__(self, class_):
        pass

    def manage(self, class_, manager):
        setattr(class_, '_default_class_manager', manager)

    def dispose(self, class_, manager):
        delattr(class_, '_default_class_manager')

    def manager_getter(self, class_):
        def get(cls):
            return cls._default_class_manager
        return get

    def instrument_attribute(self, class_, key, inst):
        pass

    def post_configure_attribute(self, class_, key, inst):
        pass

    def install_descriptor(self, class_, key, inst):
        setattr(class_, key, inst)

    def uninstall_descriptor(self, class_, key):
        delattr(class_, key)

    def install_member(self, class_, key, implementation):
        setattr(class_, key, implementation)

    def uninstall_member(self, class_, key):
        delattr(class_, key)

    def instrument_collection_class(self, class_, key, collection_class):
        global collections
        if collections is None:
            from sqlalchemy.orm import collections
        return collections.prepare_instrumentation(collection_class)

    def get_instance_dict(self, class_, instance):
        return instance.__dict__

    def initialize_instance_dict(self, class_, instance):
        pass

    def install_state(self, class_, instance, state):
        setattr(instance, '_default_state', state)

    def remove_state(self, class_, instance):
        delattr(instance, '_default_state')

    def state_getter(self, class_):
        return lambda instance: getattr(instance, '_default_state')

    def dict_getter(self, class_):
        return lambda inst: self.get_instance_dict(class_, inst)
