Active Record with Entity Framework - vb.net

Question

I'm working on a project that was built using ADO.NET (raw sql) and Active Record pattern. I am slowly moving it away from ADO.NET to Entity Framework Code First 4.3.
Here is an example of the pattern. The interface is a static Load and an instance Save (and Delete -- not shown).
Public Class Part
Public Property Id as Integer
Public Shared Function Load(_id As Integer) As Part
Using context As New DataContext()
Return context.Find(_id)
End Using
End Function
Public Sub Save()
Using context As New DataContext()
If Id = 0 Then
context.Parts.Add(Me)
Else
context.Entry(Me).State = Data.EntityState.Modified
End If
context.SaveChanges()
End Using
End Sub
End Class
I realize Active Record is not ideal for EF but I'd like to make it work to remove all of the ADO.NET code while not touching the rest of the code.
This mostly works, but I've run into an issue I don't know how to solve. In order to keep Foreign Keys in sync we handle it like such:
Public Sub Save()
ParentPart = Part.Load(ParentPartId)
ChildPart = Part.Load(ChildPartId)
Using context = New iTracContext()
If bid = 0 Then
context.BillOfMaterials.Add(Me)
Else
context.Entry(Me).State = Data.EntityState.Modified
End If
context.SaveChanges()
End Using
End Sub
This makes sure EF doesn't complain that we have non-matching relationships -- the Id always wins.
The issue is that its throwing an exception now when I save.
An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key.
This is thrown from the line:
context.Entry(Me).State = Data.EntityState.Modified
How is anything in the ObjectStateManager for this context? It is brand new and should be empty, no?
If I remove the two Part.Load(...) lines it works fine.
Is there some type of change tracker that lives outside the context that I'm not aware of? That seems like it would kill any attempt at the Active Record pattern.
I'm also open to any suggestions on how to make Active Record work with EF. The context.Entry line is terrible but I don't know what else to do.
Telling me not to do Active Record isn't helpful, but feel free.

Answer 1

I believe Entity Framework may still be tracking the object from the context you loaded it from, because you create a new context for each Load and Save call. If this is the case, try detaching the objects after you load them:
Public Shared Function Load(_id As Integer) As Part
Using context As New DataContext()
Part part = context.Find(_id)
context.Entry(part).State = EntityState.Detached ' Detach from the initial context
Return part
End Using
End Function