Find and retract orphans in Datomic

not_unique.clj

(ns datomic-manual-tests.not-unique
  (:require [datomic.api :as d]))

(def db-uri "datomic:mem://not-unique")
(d/create-database db-uri)
(def conn (d/connect db-uri))

(def schema
 [{:db/id (d/tempid :db.part/db)
   :db/ident :parent/child
   :db/valueType :db.type/ref
   :db/cardinality :db.cardinality/one
   :db.install/_attribute :db.part/db}
  {:db/id (d/tempid :db.part/db)
   :db/ident :parent/name
   :db/valueType :db.type/string
   :db/cardinality :db.cardinality/one
   :db.install/_attribute :db.part/db}
  {:db/id (d/tempid :db.part/db)
   :db/ident :child/name
   :db/valueType :db.type/string
   :db/cardinality :db.cardinality/one
   :db.install/_attribute :db.part/db}])

@(d/transact conn schema)
@(d/transact conn [{:db/id (d/tempid :db.part/user -1)
                    :parent/name "Bill"
                    :parent/child (d/tempid :db.part/user -2)}
                   {:db/id (d/tempid :db.part/user -2)
                    :child/name "Jill"}])

(def bill-eid
  (d/q '[:find ?e .
         :where
         [?e :parent/name "Bill"]]
    (d/db conn)))

@(d/transact conn [{:db/id (d/tempid :db.part/user -3)
                    :child/name "Jill"}
                   [:db/add bill-eid :parent/child (d/tempid :db.part/user -3)]])

(d/q '[:find ?name (count ?p)
       :where
       [?p :child/name ?name]]
  (d/db conn))
;; [["Jill 2"]]

(def orphan-q
  '[:find ?p ?name
    :where
    [?p :child/name ?name]
    (not [_ :parent/child ?p])])


(def q-results (d/q orphan-q (d/db conn)))

(def retractions
  (mapv (fn [[eid cname]]
          [:db.fn/retractEntity eid]) q-results))

(def db-after (:db-after @(d/transact conn retractions)))

(d/q orphan-q db-after)
;#{}