Question

I am trying to insert a record. This code worked but has stopped working I don’t know why. Here is the code:

using (SAASDataContext dc = new SAASDataContext())
{
    tblAssessment a2 = new tblAssessment();

    a2.AssessmentCentreId = centreId;
    a2.AttemptNumber = 1;

    dc.tblAssessments.InsertOnSubmit(a2);
    dc.SubmitChanges();

    CurrentAssessmentId = a2.AssessmentId;
}

The code compiles but throws the exception below on the dc.SubmitChanges(); line.

Exception thrown:

An attempt has been made to Attach or Add an entity that is not new,
perhaps having been loaded from another DataContext. This is not
supported.

Notes:
AssessmentCentreId is a foreign key on tblCentre, centreId is a valid existing centre id,
AssessmentCentreId and AttemptNumber are the only not null fields all other columns allow nulls.

I have googled but all the results seem to pertain to people trying to attach entities pulled from other disconnected DataContext’s I’m not doing that so I’m stumped.

UPDATE:

Adding

dc.DeferredLoadingEnabled = false;

at the top of the using block makes it work, but I’d like to know why coz I have no idea at the moment sufficiently advanced technology being indistinguishable from magic right now 🙂

Answer 1

The issue is that the Centre object doesn’t exist in the context. It’s in the db, but not “in your hand” with a2. Try this:

a2.AssessmentCentre = dc.AssessmentCentres.SingleOrDefault(
    d=>d.AssessmentCentreId.Equals(centreId));

The AssessmentCentre object will then exist in the context, which means there will be no problem with attaching it to a2.