Datomic user->group memberships

gistfile1.clj

(use '[datomic.api :only (q db) :as d])
(def uri "datomic:mem://user-groups2")
(d/create-database uri)
(def conn (d/connect uri))

(d/transact
 conn
 [{:db.install/_attribute :db.part/db
   :db/id #db/id[:db.part/db]
   :db/ident :user/name
   :db/unique :db.unique/value
   :db/index true
   :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 :group/name
   :db/unique :db.unique/value
   :db/index true
   :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 :user/memberships
   :db/valueType :db.type/ref
   :db/cardinality :db.cardinality/many}
  ])

(let [[chess-club tennis-club sally bob chris] (repeatedly #(d/tempid :db.part/user))]
  (d/transact conn
              [{:db/id chess-club :group/name "chess club"}
               {:db/id tennis-club :group/name "tennis club"}
               {:db/id sally :user/name "sally"}
               {:db/id bob :user/name "bob"}
               {:db/id chris :user/name "chris"}
               {:db/id bob :user/memberships [chess-club tennis-club]}
               {:db/id chris :user/memberships [chess-club]}
               {:db/id sally :user/memberships [tennis-club]}]))

;; find sally
(q '[:find ?m :where [?m :user/name "sally"]] (db conn))

;; find everyone in chess club
(q '[:find ?un ?e :where [?g :group/name "chess club"] [?e :user/memberships ?g] [?e :user/name ?un]] (db conn))