I’m building a booking engine for a car hire place.
I have a Booking l2s object, which has a Car and Location objects (and subsequent FK CarID / LocationID fields).
During the first step of the booking process, I new up a Booking() class. This is passed along in a session to the subsequent pages.
As the user proceeds through the process, the CarID, and LocationID properties are set, however because the Booking object has not been persisted back to the database, I cannot reference Booking.Car.CarModel for example.
So what I am doing is setting it explicitly:
Booking.Car = DB.Car.Where(x => x.id == Booking.CarID).Single();
etc.
When it comes time to save the Booking, it throws a:
An attempt has been made to Attach or
Add an entity that is not new, perhaps
having been loaded from another
DataContext. This is not supported.
So it would seem it’s thinking the Booking entity is not new. If I try and null out the values I’ve explicity set (Booking.Car = null), it throws another error:
An attempt was made to remove a relationship between a Car and a Booking. However, one of the relationship’s foreign keys (Booking.CarID) cannot be set to null.
And now I’m stumped…
Final Solution
What I ended up doing (after trying a bunch of different things) was just prior to saving the Booking, I reload the Car and Location objects from the current context. Not exactly efficient, but meh.
I am quite sure you have a problem with your data conext handling. Do you create one per request? If the answer is yes, the problem is that your objects are associated with different contexts. You will have to detach them from the context you used to fetch them from the database and reattch them to the context you want to use for storing them.