datomic-rule-query.clj

(require '[datomic.api :as d])
(def uri "datomic:mem://foo")
(d/delete-database uri)
(d/create-database uri)
(def conn (d/connect "datomic:mem://foo"))
(def test-schema [#:db{:ident :list/head,
                       :valueType :db.type/string,
                       :cardinality :db.cardinality/one,
                       :unique :db.unique/identity}
                  #:db{:ident :list/next,
                       :valueType :db.type/ref,
                       :cardinality :db.cardinality/one}
                  #:db{:ident :list/value,
                       :valueType :db.type/long,
                       :cardinality :db.cardinality/one,
                       :unique :db.unique/identity}])
@(d/transact conn test-schema)

(def some-values (for [i (range 100)]
                   {:list/value i}))
@(d/transact conn some-values)

(defn lv [{:keys [:list/value]}]
  [:list/value value])

(->> (reduce (fn [[agg prev] current]
               [(if-not prev
                  (conj agg [:db/add (lv current) :list/head "the-head"])
                  (conj agg [:db/add (lv prev) :list/next (lv current)]))
                current])
             [[] nil] (vec some-values))
     first
     (d/transact conn)
     deref)

(def list-head
  '[[(list-head [?x] ?head)
     [?x :list/head]
     [(identity ?x) ?head]]
    [(list-head [?x] ?head)
     [?y :list/next ?x]
     [list-head ?y ?head]]])

(time
 (d/q '[:find ?head
        :in $ % ?value
        :where
        [?head :list/head]
        [?elem :list/value ?value]
        [list-head ?elem ?head]]
      (d/db conn)
      list-head
      99))