Cast linq results to List

Question

I have extended my entities to implement specific interfaces for its type. I am trying to perform the following query:

 var results = from x in context.MyEnt         


        

Answer 1

You can do the cast on the client, bypassing the entity framework query translation layer by calling AsEnumerable extension method:

return results.Any()
       ? results.AsEnumerable().Cast<IApplicationEntity>().ToList() 
       : null;

However, it's better to reverse the order of doing the Count check:

var list = results.AsEnumerable().Cast<IApplicationEntity>().ToList();
return list.Count == 0 ? null : list;

Answer 2

return results.Count() > 0 ? 
results.Select(result => (IApplicationEntity)result)
.ToList() : null;

Answer 3

If you want to cast your results to a complex type, you need to force the code to use LINQ to Objects rather than LINQ to Entities.

Calling the AsEnumerable extension method before the cast is the trick here.

Try the following:

var results = from x in context.MyEntityTable
              where x.AProperty == AValue
              select x;

return results.AsEnumerable().Cast<IApplicationEntity>().ToList();

Also note that it's not wise to check Count() on the enumerable, since it means the collection is iterated over twice.