tempdat.clj

(ns tempdat
  "Minimal example of an unexpected Datomic behavior"
  (:require [datomic.api :as d]))

(def uri "datomic:mem://temp")
(d/delete-database uri) ; ensure fresh start
(d/create-database uri)

(def conn (d/connect uri))

(def schema-tx
  [{:db/id #db/id[:db.part/db]
    :db/ident :foo/bar
    :db/valueType :db.type/string
    :db/cardinality :db.cardinality/one
    :db.install/_attribute :db.part/db}])

@(d/transact conn schema-tx)

(def seeds
  [{:db/id #db/id[:db.part/user -1000001], :foo/bar "whatever"}])

@(d/transact conn seeds)

;; This returns a set with one item, as expected
(println "With attribute:"
         (d/q '[:find ?e :where [?e :foo/bar "whatever"]] (d/db conn)))

;; But this returns an empty set, rather than (as I'd expect) a
;; set of one item
(println "Without attribute:"
         (d/q '[:find ?e :where [?e _ "whatever"]] (d/db conn)))

;; Why?