Question

How would you to convert or cast a List<T> to EntityCollection<T>?

Sometimes this occurs when trying to create ‘from scratch’ a collection of child objects (e.g. from a web form)

 Cannot implicitly convert type 
'System.Collections.Generic.List' to 
'System.Data.Objects.DataClasses.EntityCollection'

Answer 1

I assume you are talking about List<T> and EntityCollection<T> which is used by the Entity Framework. Since the latter has a completely different purpose (it’s responsible for change tracking) and does not inherit List<T>, there’s no direct cast.

You can create a new EntityCollection<T> and add all the List members.

var entityCollection = new EntityCollection<TEntity>();
foreach (var item m in list)
{
  entityCollection.Add(m);
}

Unfortunately EntityCollection<T> neither supports an Assign operation as does EntitySet used by Linq2Sql nor an overloaded constructor so that’s where you’re left with what I stated above.