In which cases do I need to create two different extension methods for IEnumerable and IQueryable?

Question

Let\'s say I need an extension method which selects only required properties from different sources. The source could be the database or in-memory collection. So I have defined

Answer 1

If your code only actually works when the objects its dealing with are loaded in memory, just supply the IEnumerable variant and let your callers decide when they want to convert an IQueryable into an in-memory IEnumerable.

Generally, you won't implement new variations around IQueryable unless you're writing a new database provider.