Why does the entity framework need an ICollection for lazy loading? - entity-framework

Question

I want to write a rich domain class such as
public class Product
{
public IEnumerable<Photo> Photos {get; private set;}
public void AddPhoto(){...}
public void RemovePhoto(){...}
}
But the entity framework (V4 code first approach) requires an ICollection type for lazy loading! The above code no longer works as designed since clients can bypass the AddPhoto / RemovePhoto method and directly call the add method on ICollection. This is not good.
public class Product
{
public ICollection<Photo> Photos {get; private set;} //Bad
public void AddPhoto(){...}
public void RemovePhoto(){...}
}
It's getting really frustrating trying to implement DDD with the EF4. Why did they choose the ICollection for lazy loading?
How can i overcome this? Does NHibernate offer me a better DDD experience?

Answer 1

I think i found the solution...See here for more details: http://social.msdn.microsoft.com/Forums/en-US/adodotnetentityframework/thread/47296641-0426-49c2-b048-bf890c6d6af2/
Essentially you want to make the ICollection type protected and use this as the backing collection for the public IEnumerable
public class Product
{
// This is a mapped property
protected virtual ICollection<Photo> _photos { get; set; }
// This is an un-mapped property that just wraps _photos
public IEnumerable<Photo> Photos
{
get { return _photos; }
}
public void AddPhoto(){...}
public void RemovePhoto(){...}
}
For lazy loading to work the type must implement ICollection and the access must be public or protected.

Answer 2

You can't insert into an IEnumerable. This applies to the EF just as much as it does to your clients. You don't have to use ICollection, though; you can use IList or other writeable types. My advice to get the best of both worlds is to expose DTOs rather than entities to your clients.

Answer 3

You can overcome this by using the ReadOnlyCollection(Of T)
public class Product
{
private IList<Photo> _photos;
public IList<Photo> Photos {
get
{
return _photos.AsReadOnly();
}
private set { _photos = value; }
}
public void AddPhoto(){...}
public void RemovePhoto(){...}
}
EDIT:
ICollection<T> => IList<T>
Hope that is what you were looking for.