Hi Bassel,
In the latest versions of Telerik OpenAccess the
Telerik.OpenAccess.Query namespace is no longer needed in order to use the Extent<T> method. The method is now part of the root
Telerik.OpenAccess namespace.
Could you please tell us which of the OpenAccess approaches you are using - the "classic" Forward/Reverse mapping wizards or the new visual designer? If you are using the new designer, you will have to use the auto-generated OpenAccessContext class to manage persistent objects instead of an object scope. Please try to give some more details on what you are trying to achieve, so we can help you further.
All the best,
Alexander
the Telerik team