Datomic transaction function for migration

migration.clj

(def run-once
 (d/function '{:lang "clojure"
               :requires [[datomic.api :as d]]
               :params [db db-fn]
               :code (when-not (d/pull db [:data.migration/done] db-fn)
                       [[db-fn]
                        [:db/add db-fn :data.migration/done "datomic.tx"]])}))

(def schema-tx
 [{:db/ident :data.migration/run-once
   :db/fn run-once
   :db/doc "First time when this function is called with a given no-param function will run that function and annotate it with :data.migration/done. Subsequent calls with the same function are no-ops."}
  {:db/ident :data.migration/done
   :db/valueType :db.type/ref
   :db/cardinality :db.cardinality/one
   :db/doc "If function has been run with :data.migration/run-once this attribute will reference the transaction where it happened."}])