Entity Framework - Crash on Detaching list of objects

Question

I am working on a winform application with EF 4.0.

Below code, crashes with issue 'The object cannot be detached because it is not attached to the ObjectStateManager.' when it tries to detach the list from context.

public List<Users> FindUserList()
        {
            List<Users> lstUsers = null;
            var q = from c in context.Users
                    select c;
            lstUsers = q.ToList();
            //context.Detach(lstUsers.First());
            context.Detach(lstUsers);
            return lstUsers;
        }

Surprisingly, it works fine if I detach only one object from the list as I have done in the commented code.

Can someone tell, why it crashes when it tries to detach a list? Also, How can we detach all objects of the list?

score 1 · Answer 1 · answered Sep 29 '11 at 09:23

1

That is because lstUsers is not an entity. But the entity returned by lstUsers.First() is tracked by EF.

answered Sep 29 '11 at 09:23

Eranga

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So, you mean we can NOT detach a collection of objects directly?? – user899055 Sep 29 '11 at 09:24
Can someone please reply asap – user899055 Sep 29 '11 at 09:40
1

@user899055 you will have to do one by one. You can write an extension method to do that – Eranga Sep 29 '11 at 09:42

score 0 · Answer 2 · answered Oct 21 '15 at 06:13

Try adding .AsNoTracking() to the Users DbSet to detach it from the context. See below.

List<Users> lstUsers = null;
var q = from c in context.Users.AsNoTracking()
       select c;
 lstUsers = q.ToList();
 return lstUsers;

MSDN Reference
https://msdn.microsoft.com/en-us/library/gg679352(v=vs.103).aspx

StackOverflow question regarding AsNoTracking What difference does .AsNoTracking() make?

Entity Framework - Crash on Detaching list of objects

2 Answers2