Question

I’m using Entity Framework 4.1 (database first, e.g “old school”), and i’m using POCOs in an ASP.NET MVC 3 web app.

I’ve got a 1 – 0..1 relationship between Foo and Bar, backed by a nullable int on the Foo table.

My POCO’s look like this:

public class Foo
{
   public Bar Bar { get; set; 
}

public class Bar
{
   public int BarId { get;set; }
}

Now, i have a Foo which already exists in the system, but BarId is null.

Now i’m trying to associate that Foo with an existing Bar.

This is the code i’ve got:

var existingBar = _repo.GetBar(2);
var existingFoo = _repo.GetFoo(1);
existingFoo.Bar = existingBar;

But behind the scenes, EF is adding a new Bar. Why?

I also tried this:

existingFoo.Bar = new Bar { BarId = 2 }; 

E.g the “stub technique”, but results in EF complaining about empty columns (because again, it’s trying to create a “new” Bar).

I’m sure i’ve done this before – i just hope the solution i ended up going with wasn’t “use a SP”.

As i mentioned – i’m using POCO’s, so i don’t have direct access to the DbContext or ObjectContext from my controller.

Any advice?

Answer 1

I suspect that’s because

DbContext API and its DbChangeTracker doesn’t provide a way to change a state of Independent association (we must convert DbContext back to ObjectContext and change the state in ObjectStateManager).

The above was quoted from Ladislav Mrnkva’s blog post. Try to define the BarId property in your Foo class and see if it causes the context to work properly.