Thank you for your interest in Telerik DataAccess.
I think the problem in your case is the query and the respective joins. Can you please try to see if the following query fulfills your requirements?
IQueryable<BESTELLKOPF> query = from b
b.Lieferant == 69
In this case we are generating an outerjoin to the orderXml table and all the orders where the orderXml reference is null are returned.
Can you try to see if you are still experience the duplicate object key problems?
Hope this helps.
Do come back in case you have any other question.
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