C# – LINQ to SQL Basic insert throws: Attach or Add not new entity related exception

asp.netclinq-to-sql

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 🙂

Best Answer

This was bugging me as well. I did some searching and found a lot of confusion and some sloppy work-arounds regarding detached entities. I then found a nice solution on codeplex that has solved the immediate issue and has greatly extended linq2sql functionality. Its a small class thats really easy to implement and forms an EntityBase for your projects dbml's.

Here is the offical description and link. LINQ to SQL Entity Base is a simple base class that is primarily designed to support LINQ to SQL in a disconnected way, which is one of the shortcomings of the LINQ to SQL technology at the present time. This is highly useful in an n-Tier, distributed or ASP.NET environment where disconnected functionality is relavent.

http://linq2sqleb.codeplex.com/

Hope this helps anyone who is having similar.

Jerome Vernon

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