C# – According to Msdn GridView.DataKeyNames must be set if we want to update database

All of the DataKey values will always be passed to the Delete method because the fields named by DataKeyNames are intended to be the field or fields that uniquely identify that item in the GridView. They're often used for more than that to easily maintain extra fields on a per-row basis in ViewState as you are here, but doing so has the side-effect that you're seeing with the ObjectDataSource methods.

To answer your original question, no, you can't have Category be in DataKeyNames without having it be passed to the Delete method. You could maintain the value in ViewState by putting the value in a hidden input in your Template Column, though. It would be more work to get that value out than to ignore the parameter to the Delete method, though.

I guess this is too late... But first, you are trying to get data keys right after data retrieval and not after data bind. DataKeys do not get populated until DataBind.

Second, data keys do not store new post-update values. They are copies of what was available during binding, stored in the view state, and used primarily to locate records after a post back w/o doing another bind.