datomic query to return the tx at which an entity or its components were last touched

last-touched-tx.clj

(require '[datomic.api :as d])
(defn last-touched-tx
  "Return the tx of the oldest assertion on `entity` or any of its components."
  [db entity]
  (or (d/q '[:find (max ?tx) .
             :in $ % ?root
             :where
             (component-entities ?root ?ce)
             (union ?root ?ce ?e)
             [?e _ _ ?tx]]
        db
        '[[(component-attr? [?a])
           [?a :db/isComponent true]
           [(datomic.api/entid $ :db.type/ref) ?reftype]
           [?a :db/valueType ?reftype]]
          [(rebind [?a] ?b)
           [(identity ?a) ?b]]
          [(union [?a ?b] ?c)
           (rebind ?a ?c)]
          [(union [?a ?b] ?c)
           (rebind ?b ?c)]
          [(component-entities [?e] ?ce)
           [?e ?a ?ce]
           (component-attr? ?a)]
          [(component-entities [?e] ?ce)
           [?e ?a ?r]
           (component-attr? ?a)
           (component-entities ?r ?ce)]]
        (d/entid db entity))
    0))