ICollection<T> Vs List<T> in Entity Framework

Question

I only watched a few webcasts before I went head first in to designing a few Entity Framework applications. I really didn't read that much documentation and I feel like I am suffering for it now.

I have been using List<T> in my classes, and it has worked great.

Now I have read some documentation and it states that I should have been using ICollection<T>. I changed to this, and it didn't even cause a model context change. Is this because both List<T> and ICollection<T> inherit IEnumerable<T>, and that is what is actually required for EF?

However, if this is the case, why doesn't the EF documentation state that it requires IEnumerable<T> instead of ICollection<T>?

In any case, are there any downsides to what I have done, or should I change it?

Answer 1

Entity Framework would use ICollection<T> because it needs to support Add operations, which are not part of the IEnumerable<T> interface.

Also note that you were using ICollection<T>, you were merely exposing it as the List<T> implementation. List<T> brings along with it IList<T>, ICollection<T>, and IEnumerable<T>.

As for your change, exposing via the interface is a good choice, despite List<T> working. The interface defines the contract but not the implementation. The implementation could change. In some instances, perhaps the implementation could be a HashSet<T>, for example. (This is a mindset you could use for more than just Entity Framework, by the way. A good object-oriented practice is to program towards the interface and not the implementation. Implementations can and will change.)