Is there a flexible method in Rails to convert string to XXX : Thanks to view this question,
actually **XXX** is not real XXX,
I just don't know how to call it.
What I wanna know is :

`string = "id: 2"`

How can I use

`User.where(string)`

Thanks to talented friends, hope useful answer!
BTW, pls let me know how to call the **XXX** :)