demo.clj

(ns dato.demo
  (:require [datomic.api :as d])) ; datomic version 0.9.6024

(def url "datomic:mem://test-db")

(def conn (do (d/delete-database url)
              (d/create-database url)
              (d/connect url)))

(def schema
  [#:db{:ident :e/a, :cardinality :db.cardinality/one, :valueType :db.type/string}
   #:db{:ident :e/b, :cardinality :db.cardinality/one, :valueType :db.type/ref}
   #:db{:ident :other/id, :cardinality :db.cardinality/one, :valueType :db.type/string :unique :db.unique/identity}
   #:db{:ident       :e/a+b,
        :cardinality :db.cardinality/one,
        :valueType   :db.type/tuple,
        :tupleAttrs  [:e/a :e/b],
        :unique      :db.unique/identity}])

@(d/transact conn schema)

@(d/transact conn [{:db/id    "ref"
                    :other/id "other"}
                   {:e/a "a"
                    :e/b "ref"}])

(def db (d/db conn))

(println (d/pull db '[:*] [:e/a+b ["a" [:other/id "other"]]]))
; => #:db{:id nil} !

(println (d/pull db '[:*] [:e/a+b ["a" (:db/id (d/pull db [:db/id] [:other/id "other"]))]]))
; => {:db/id 17592186045419, :e/a a, :e/b #:db{:id 17592186045418}, :e/a+b [a 17592186045418]}