Hi JC Wu,
In order to update an existing entity you need to load it in memory first.
This can be achieved using various operations like the first LINQ query that you have posted.
OpenAccess does not allow creation of new entity instances and using them to update existing one.
If you want to mark one to be updated via the Attach mechanism you will have to detach the same entity first.
For more information about our attach-detach functionality please see this online article
If you have any further questions, do not hesitate to contact us again.
the Telerik team