How to revert changes on detached entities

Question

Here's the flow of the program:

1. Fetch a list of entities and use them. This will disconnect/detach all entities from the context.
2. Make changes on one of the entities and save it. I'm loading the entity from the context and apply the changes (scalar properties and relational) of the detached entity to the freshly loaded entity.

3. I have a feature where the user can revert all changes made on the disconnected entity. Here's the code I'm using:

       public async Task RevertChanges()
   {
       using (var db = new TwinTailDb())
       {
           //Fansubs.Clear();
   
           if (db.Entry(this).State == EntityState.Detached && Id != 0)
           {
               db.ArchiveEntries.Attach(this);
               await db.Entry(this).ReloadAsync();
           }
   
           //await db.Entry(this).Collection(a => a.Fansubs).LoadAsync();
       }
   }
   

However, when I attach the detached entity, it throws this exception:

Additional information: Attaching an entity of type 'TwinTail.Entities.ArchiveEntry' failed because another entity of the same type already has the same primary key value. This can happen when using the 'Attach' method or setting the state of an entity to 'Unchanged' or 'Modified' if any entities in the graph have conflicting key values. This may be because some entities are new and have not yet received database-generated key values. In this case use the 'Add' method or the 'Added' entity state to track the graph and then set the state of non-new entities to 'Unchanged' or 'Modified' as appropriate.

Note that the context is automatically disposed because I'm using the using statement.

I'm not sure why it even there is a conflict in the primary key since I didn't even load another entity since the previous context was already disposed.

Also, if I skip step 2 where I save all changes in the entity, it doesn't throw an exception. I'm left with thinking that somehow it's still being tracked .

EDIT: Here's what happens when I skip attaching, proving that the entity is really detached.

Additional information: Member 'ReloadAsync' cannot be called for the entity of type 'ArchiveEntry' because the entity does not exist in the context. To add an entity to the context call the Add or Attach method of DbSet.

Seriously, what's happening :(

Answer 1

Some actions on the entities that involve context might change the state to Attached. It could happen when passing an entity to a method in context. Try placing a breakpoint with condition to break when Entity state changes, and make sure that entity does not get attached before you actually call attach, as a side effect of other actions. If that is the case, than you're trying to attach an entity that is already attached, which should cause an exception.

Answer 2

Answering my own question.

The main problem was that the way I handled the lifetime of context is wrong. Also, attaching an entity that was loaded from another context will surely throw an error. Entities that are loaded in a context should only be used in that context.

My context is too short-lived. I'll adjust its lifetime so that there's one context for every transaction (database process).

Here's a very detailed article on how to solve/design your architecture: http://mehdi.me/ambient-dbcontext-in-ef6/

After fixing the architecture, reloading/reverting an entity can simply be done by calling:

DbContext.Entry(entity).Reload();