Eager-loading & LINQ to Entities

Question

So far as I gathered, LINQ to entities encourages eager loading with Load() or Include(). However, I wonder where should the eager loading take place in a multi-layered application?

Is it correct for the data-access layer (a repository class encapsulating the Entity instance) to have a generic Item GetItem(int id) function, and in business logic layer do

Item item = dbRepository.GetItem(itemId);
if (!item.itemDetails.IsLoaded)
 item.itemDetails.Load()

Or should the repository class have different explicit functions that load different foreign relations, therefore return Item of eager-loaded relations?

Many thanks!

Edit: Example - http://www.asp.net/learn/mvc/tutorial-29-cs.aspx

public Contact GetContact(int id)

This function returns a Contact entity type. However, depends on the business logic needs, we may want to Load() or Include() different foreign relations of the Contact entity. Does this requirement mean we need more overloaded GetContact() methods with parameters indicating which relations to load, or simply do the Load() in business logic?

Answer 1

For the most part, I don't do either one. Instead, I use LINQ to map my entity types to presentation model types. In this case, you don't have to think about loading at all. For example:

var presentationModel = (from entity in Repository.Entities
                         select new PresentationEntity ()
                         {
                             Prop = entity.Prop,
                             ChildProp = entity.Child.Prop
                         }).First();

Notice that I did not have to think about loading Child. LINQ to entities does this for you when you project onto a different type.