NavigationProperty null on added foreign key

Question

Whenever I add a foreign key entity to my previous entity by setting the ForeignKey-ID, the associated object is null.

Let me explain this:

In a previous step I've set the AddressId property to 28 and have saved the entity context by calling context.SaveChanges().

Now why is AddressId filled, but Address as the NavigationProperty (which should be an Address object of the Address table where Address.Id == 28) is null?

Answer 1

Entity Frameworks (EF) work this by design. Updating the foreign key never updates the navigation property.

However, updating the navigation property will update the key. Also note that in this case the Address entity should come from the same context. If not .SaveChanges() will consider the Address entity as new and try to add it in the database.

As to the question of which method is better, well, it depends!
- Updating the Key is straightforward and is what we have been doing all along using Data Transfer Objects (DTOs) or even plain SQL. So is easier for newcomers to EF to grasp and use.
- Updating the navigation property is where you truly get an object based data model. The code looks cleaner and more readable. However you need to be very careful with the Context. In my little personal experience with EF, I find that trying to update the navigation property brings more complexity than value, especially in a multi-tier architecture where the Context is hidden behind the Data Access layer.

The most important benefit of EF, in my opinion, is in query operations using LINQ-to-Entities. I have compile-time syntax check for my queries and strong typing. I can easily create an object-based result set with multiple levels of children, data-bind ready without any additional code. I rarely write SQL anymore.

Answer 2

I sorta fixed this by re-creating my entities and reloading then. This seems to work and re-fetch the n:m relationship navigation properties. Weird.