~{func} :: (P.PersistMonadBackend (b (HandlerT master IO)) ~ P.PersistEntityBackend ~{entityName e}, 
                b ~ YesodPersistBackend master,
                P.PersistQuery (b (HandlerT master IO)),
                P.PersistUnique (b (HandlerT master IO)),
                YesodPersist master)
            => ~{entityName e} -> HandlerT master IO Bool