Datomic multiple attribute key example

core.clj

(ns myupsert.core
  (require [datomic.api :as d]))

(def schema
  [
   {:db/id #db/id [:db.part/db]
    :db/ident :product/name
    :db/valueType :db.type/string
    :db/cardinality :db.cardinality/one
    :db.install/_attribute :db.part/db}
   {:db/id #db/id [:db.part/db]
    :db/ident :product/version
    :db/valueType :db.type/string
    :db/cardinality :db.cardinality/one
    :db.install/_attribute :db.part/db}
   {:db/id #db/id [:db.part/db]
    :db/ident :product/price
    :db/valueType :db.type/double
    :db/cardinality :db.cardinality/one
    :db.install/_attribute :db.part/db}
   {:db/id #db/id [:db.part/user]
    :db/ident :upsertProduct
    :db/fn #db/fn
    {:lang :clojure
     :params [db m]
     :code (if-let [id (ffirst
                        (d/q '[:find ?e
                               :in $ ?n ?v
                               :where
                               [?e :product/name ?n]
                               [?e :product/version ?v]]
                             db (:product/name m) (:product/version m)))]
             [(-> (dissoc m :product/name :product/version)
                  (assoc :db/id id))]
             [m])}}
   ])

(defn init-db []
  (let [uri "datomic:mem://test"
        _ (d/create-database uri)
        conn (d/connect uri)
        _ (d/transact conn schema)]
    conn))

(defn get-product [name version conn]
  (->> (d/q '[:find ?e
              :in $ ?n ?v
              :where [?e :product/name ?n] [?e :product/version ?v]]
            (d/db conn) name version)
       (map first)
       (map #(d/entity (d/db conn) %))
       (map d/touch)))

(comment
  (def conn (init-db))
  (d/transact conn [[:upsertProduct {:db/id #db/id [:db.part/user]
                                     :product/name "Foo"
                                     :product/version "1.1"
                                     :product/price 12.34}]])
  (get-product "Foo" "1.1" conn)
  (d/transact conn [[:upsertProduct {:db/id #db/id [:db.part/user]
                                     :product/name "Foo"
                                     :product/version "1.1"
                                     :product/price 56.78}]])
  (get-product "Foo" "1.1" conn)
  )

Nicely done. But this upsert doesn't work if you try to upsert two products in the same transaction. Executing

(d/transact conn [[:upsertProduct {:db/id (d/tempid :db.part/user)
                                   :product/name "Foo"
                                   :product/version "1.1"
                                   :product/price 12.34}]
                  [:upsertProduct {:db/id (d/tempid :db.part/user)
                                   :product/name "Foo"
                                   :product/version "1.1"
                                   :product/price 12.56}]])

leads to two products with the same :product/name and :product/version. The reason for this is that both :upsertProduct functions get the same database from the start of the transaction.

Yes, you are right. And AFAIK this can not be solve using a transaction function. This topic is discussed here: https://groups.google.com/d/msg/datomic/dhzwweFSiso/lqET7Isa6XcJ

Yes, you are right. And AFAIK this can not be solve using a transaction function.

But I can live with that. I think it's more of a logical limitation on what a transaction is supposed to be than on Datomic's feature set. I'd love to see a Gist for a utility method for breaking up transactions into multiple ones based on compound keys before I have to work it out myself, lol.