Returning IEnumerable vs. IQueryable

Question

What is the difference between returning IQueryable vs. IEnumerable, when should one be preferred over the other?

Answer 1

In general terms I would recommend the following:

• Return IQueryable if you want to enable the developer using your method to refine the query you return before executing.

• Return IEnumerable if you want to transport a set of Objects to enumerate over.

Imagine an IQueryable as that what it is - a "query" for data (which you can refine if you want to). An IEnumerable is a set of objects (which has already been received or was created) over which you can enumerate.