Attaching detached entries with same key - entity-framework-4.1

Question

I am using Code First Entity Framework 4.1. The two entities that I am using are "State" and "User". Each State entry has a "CreatedBy" User and "ModifiedBy" User properties as given below.
public class State {
public virtual User CreatedBy { get; set; }
public virtual User ModifiedBy { get; set; }
}
The User entity doesn't have any back reference to State entity, that is State => User is "Unidirectional".
The problem occurs when there is a detached State entity which has same "CreatedBy" and "ModifiedBy" User properties. When I try to attach State Entity to the dbContext, the EntityFramework complains that duplicate entry found by ObjectStateManager. I was looking for a simple solution for this issue.

Answer 1

One solution would be to check if a User with the same key is already in the context and if yes, replace the detached User references in your State entity by the objects which are attached to the context. Say, state is the new State entity to attach:
if (state.CreatedBy != null)
{
var attachedCreatedBy = context.ChangeTracker.Entries()
.Where(e => e.Entity is User
&& e.Cast<User>().Entity.Id == state.CreatedBy.Id)
.Select(e => e.Entity)
.SingleOrDefault();
if (attachedCreatedBy != null)
state.CreatedBy = attachedCreatedBy;
}
if (state.ModifiedBy != null)
{
var attachedModifiedBy = context.ChangeTracker.Entries()
.Where(e => e.Entity is User
&& e.Cast<User>().Entity.Id == state.ModifiedBy.Id)
.Select(e => e.Entity)
.SingleOrDefault();
if (attachedModifiedBy != null)
state.ModifiedBy = attachedModifiedBy;
}
context.States.Attach(state); // now it should not throw an exception anymore
Well, I would not call this a "simple solution" though. But I don't know another one. If you had foreign key properties CreatedById and ModifiedById in State it would become easier. You could just set the navigation properties CreatedBy and ModifiedBy to null and only set the foreign key properties to the Ids of the related users.