es <- lift $ runDB $ select $ from $ \o -> do
            where_ (o ^. ~{entityName e}Id ==. (val ~{inputFieldRef ctx fr}))
            limit 1
            return o
        e <- case es of
            [(Entity _ e')] -> return e'    
            _ -> sendResponseStatus status404 $ A.object [ 
                    "message" .= ("Could not update a non-existing ~{entityName e}" :: Text)
                ]