Weird Constraint Exception with entity framework

Question

I'm new to the Entities framework. One week earlier I've hit the common problem of the currentcontext that throws exception if used in a non-unique manner, but that was fixed.

Today I have a new problem, a really new one because I do not even know why this is happening since I do think that I have the same code.

Here is the error that I am getting :

Entities in 'Entities.WSUser_Detail' participate in 
the 'FK_WSUser_Detail_WSCountry' relationship. 
0 related 'WSCountry' were found. 1 'WSCountry' is expected.

What's so strange about this error is that in my code I never reference any WSUser_Detail object. Does anyone has come up with that kind of error? My code is really simple :

newUser = (from user in GB.Context.WSUsers
                where user.IDUser == nFound
                select user).FirstOrDefault();

newUser.DoNotSend = false;
newUser.IP = Request.UserHostAddress;
newUser.LastDtActivity = DateTime.Now;
newUser.Language1 = GB.User.Language;
newUser.LastVersion = sVersion;
newUser.FlushNextTime = false;

GB.Context.SaveChanges();

The error occurs on SaveChanges()

Absolutely no WSUser_Detail is being called in my code... so I wonder why should he ask for a reference that is on an object that is never called (but exists in the Entities Context).

Any idea?

The weird thing is that I do not had this problem before even if the code didn't seem to have changed.

I updated the Model.edmx to be sure that it's not the cause, but it still does not work, I've checked many times and the error shouldn't come AT ALL since I do not have any WSUser_Detail object.

Answer 1

At the database level, I would guess that you have a foreign key constraint on a field that is not allowed to be NULL .. and you the resulting model has a relationship between the WSCountry and WSUser tables.

It looks like you could be trying to save an invalid entity - one that does not satisfy your constraints..

My guess would be that your WSUser is required to have a WSCountry entity set. Is there a WSUser.WSCountry property to set ?

If my hunch is correct - make sure that this is set before saving.

By the way - 'FK_WSUser_Detail_WSCountry' does not suggest an object - it is referring to a relationship/FK constraint set up in your database. Entity Framework uses these constraints to guess how your entities should be related..

Answer 2

With this little SQL script which inspects the sys system catalog views, you should be able to find out which database constraint between which two tables (and their columns) is involved in this problem - check it out, most likely, this is a required reference, e.g. you cannot leave it empty (and you probably do in your code right now).

SELECT
    fk.name ,
    t1.Name 'Parent table',
    c1.Name 'Parent column',
CASE WHEN c1.is_nullable = 0 THEN 'No' ELSE 'Yes'
END AS 'Parent column nullable',
    t2.Name 'Referenced table',
    c2.Name 'Referenced column'
FROM 
    sys.foreign_keys fk
INNER JOIN 
    sys.foreign_key_columns fkc ON fk.object_id = fkc.constraint_object_id
INNER JOIN 
    sys.tables t1 ON fkc.parent_object_id = t1.object_id 
INNER JOIN 
    sys.tables t2 ON fkc.referenced_object_id = t2.object_id
INNER JOIN 
    sys.columns c1 ON t1.object_id = c1.object_id AND fkc.parent_column_id = c1.column_id
INNER JOIN 
    sys.columns c2 ON t2.object_id = c2.object_id AND fkc.referenced_column_id = c2.column_id
WHERE 
    fk.name = 'FK_WSUser_Detail_WSCountry'

This should give you the parent table and column as well as the referenced table and column - e.g. the two parties involved in your foreign key relationship.

That should hopefully clear up what piece of the puzzle you're missing.

Answer 3

Your model (EDMX) says that there is a 1:1 relationship between WSUser and WSUser_Detail, but your question implies that you expect the relationship to be 1:0..1, so either your own understanding or your model is incorrect. If the model has the cardinality of the relationship at 1:1, then the Entity Framework will check this whenever you create or save a WSUser entity. This is the source of the error you are seeing.

Because your question implies that this is the wrong cardinality for this relationship, you probably want to go and fix the EDMX. To do this, find the FK_WSUser_Detail_WSCountry association in the Model Browser. Click that, and expand the two End properties in the Properties window. Change the Multiplicity of the appropriate End.

Answer 4

I finaly found what the problem was!

I was using a global Context as shown here. But in some previous tests I added a user detail that wasn't containing any wscountry reference that is required. So it first ran into an exception, which is what I could expect.

The real problem is that whenever an invalid entity object is added with the method AddTo(entityObj), any further call to SaveChanges() will try to add that object into the context, even if the page that caused the problem does not exist anymore since the Context object was "corrupted".

So every call to SaveChanges() would be denied by an Exception after any AddTo with an invalid entity object...

My question would be : is it possible to have an information like the validity of the entity BEFORE trying to add it in the used context? Because fatal error like this are logical but hard to understand since it's showing an error that was done several hours ago (when working on an ASP.Net project using a global context).