get.clj

;; bin/repl with datomic-free-0.8.3664
(use '[datomic.api :only [q db] :as d])

(def uri "datomic:mem://future")

(d/create-database uri)

(def conn (d/connect uri))

;; balance attr
@(d/transact conn [{:db/id (d/tempid :db.part/db)
                    :db/ident :account/balance
                    :db/valueType :db.type/long
                    :db/cardinality :db.cardinality/one
                    :db.install/_attribute :db.part/db}])

;; create entity
(def eid (-> @(d/transact conn [{:db/id (d/tempid :db.part/user)
                                 :account/balance 100}])
             :tempids
             first
             val))


;; async happy path
(def ta1 (d/transact-async conn [[:db.fn/cas eid :account/balance 100 200]]))

(prn "ta1 result: " @ta1)

(prn "account balance: " (:account/balance (d/entity (db conn) eid)))
;; => 200

;; async fail path
(def ta2 (try (d/transact-async conn [[:db.fn/cas eid :account/balance 400 500]])
              (catch Exception e
                (prn "Won't get to here: " e))))

(try @ta2
     (catch Exception e
       (prn "Should end up here:" e)))

;; sync happy path
(def t1 (d/transact conn [[:db.fn/cas eid :account/balance 200 300]]))

;; can get the response
(prn "t1 result: " @t1)

(prn "account balance: " (:account/balance (d/entity (db conn) eid)))
;;=> 300

(def t2 (try (d/transact conn [[:db.fn/cas eid :account/balance 400 500]])
             (catch Exception e
               (prn "Should not get here, but somehow do: " e))))

(prn "t2 did not return a future")
;;;; this should have worked: 
;;(try @t2
;; (catch Exception e
;;  (prn "Wanted to check this way.")))