What will perform better? : <p>I do have 'topics',  each 'topic'  has 'questions'. Both, topics and questions,  have 'statistics'  that will be updated at every use. </p>

<p>Should I create 'questions'  as a subfield of  'topic' documents? Or I must create a collection named 'questions'  and relate it to 'topic'  using sort of a foreign key? </p>

<p>Further,  using the independent 'questions' collections will make it 'harder/expensive' to list all the questions related with a topic? </p>

<p>I'm so noob </p>
