c# - Entity Framework: A referential integrity constraint violation on many to many relationship

Question

Hey I have an application with a bunch of inproc caching and entity framework. When I want to write an update to an entity I reattach the cached copy. I track all things I've attached in the life cycle of the context so I don't try to attach them twice.

I have an error occurring on attach (very rarely in most cases this works fine and is really fast) which says the following:

A referential integrity constraint violation occurred: The property values that define the referential constraints are not consistent between principal and dependent objects in the relationship.

I've taken a really careful look at the entity which looks normal. I think this issue is due to the attachment/detachment of a foreign key when fixups runs.

Is there a good way to get any more info on this error or can it occur for reasons other than that the entity was in a state which EF wasnt expecting?

EDIT: DB Diagram (note i'm using codefirst I just used the EDMX tool to make the diagram, I've also chopped a bunch of regular properties off the model for simplicity)

Answer 1

The error could occur for the one-to-many relationship between Person and Location you apparently have in your model in addition to the many-to-many relationship. For example the following code would throw the exception:

using (var context = new MyContext())
{
    var person = new Person
    {
        CurrentLocationId = 1,
        CurrentLocation = new Location { Id = 2 }
    };
    context.People.Attach(person); // Exception
}

"The property values that define the referential constraints" are the foreign key property value CurrentLocationId and the primary key value CurrentLocation.Id. If those values are different the exception is thrown. (Having CurrentLocation as null though is allowed.)

In my opinion this exception can only be thrown for foreign key associations because only for this type of association you have properties that define referential constraints at all in your model. It cannot be thrown for independent associations. Since every many-to-many relationship is an independent association (no foreign key property in the model) my guess is that the error is not related to your many-to-many relationship, but to the one-to-many.