c# - linq : update/delete junction table have two Primary Key - 


    public void update (rate a)     {            = (from ee in datacontext.rates                 ee.users_id == a.users_id && ee.books_id == a.books_id                         select ee).singleordefault();          datacontext.submitchanges();     }

error:

violation of primary key constraint 'pk_rates'. cannot insert duplicate key in object 'dbo.rates'. duplicate key value (3, 1).


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