Using Automapper to return IQueryable

In order for Automapper to actually perform the mapping, it has to see each element in the IQueryable. Once you've iterated over a queryable, it is no longer queryable as it has been queried already.

For anyone that might miss the comment link, you can use Automapper's [QueryableExtensions][1], specifically ProjectTo. For example:

var collection = _db.Patients
     .ProjectTo<PatientDto>(_mapper.ConfigurationProvider);

This will create an IQueryable projection from the db entity.