set_with_token.clj

(def set-with-token
  (d/function
   '{:lang "clojure"
     :params [db token-attr token-value attr value]
     :code (let [e (d/q '[:find ?e .
                          :in $ ?ta ?tv
                          :where
                          [?e ?ta ?tv]]
                        db token-attr token-value)]
             (if e
               [[:db/add e attr value]
                [:db/retract e token-attr token-value]]
               (throw (ex-info (str "No entity with that token exists")
                               {token-attr token-value}))))}))