Is is possible to check if an object is already attached to a data context in Entity Framework?

Question

I am getting the following error when trying to attach an object that is already attached to a given context via context.AttachTo(...):

A

Answer 1

Try this extension method (this is untested and off-the-cuff):

public static bool IsAttachedTo(this ObjectContext context, object entity) {
    if(entity == null) {
        throw new ArgumentNullException("entity");
    }
    ObjectStateEntry entry;
    if(context.ObjectStateManager.TryGetObjectStateEntry(entity, out entry)) {
        return (entry.State != EntityState.Detached);
    }
    return false;
}

Given the situation that you describe in your edit, you might need to use the following overload that accepts an EntityKey instead of an object:

public static bool IsAttachedTo(this ObjectContext, EntityKey key) {
    if(key == null) {
        throw new ArgumentNullException("key");
    }
    ObjectStateEntry entry;
    if(context.ObjectStateManager.TryGetObjectStateEntry(key, out entry)) {
        return (entry.State != EntityState.Detached);
    }
    return false;
}

To build an EntityKey in your situation, use the following as a guideline:

EntityKey key = new EntityKey("MyEntities.User", "Id", 1);

You can get the EntityKey from an existing instance of User by using the property User.EntityKey (from interface IEntityWithKey).