datomic-fu

reset-to-many-by.edn

{:db/ident :bsu.fns/reset-to-many-by,
 :db/doc "Resets the set of entities which are related to `eid` via `ref-attr` to the set given by `val-maps`.
          Assumptions:
          * `ref-attr` is a cardinality-many, ref attribute.
          * `e` is an entity identifier for an _existing_ entity
          (you have to know whether an entity exists before using this function,
          and it's pointless to use it on a non-existing entity as opposed to just asserting all the new values.)
          * `val-maps` is a seq of transaction maps, all of which have the `v-id-attr` key provided.
          * `retract-target-entity?`: whether to call :db.fn/retractEntity on the old entities which get removed from the relationship.
          * the old values of the relationship all have the `id-attr` attribute."
 :db/id #db/id[:db.part/user],
 :db/fn #db/fn{:lang :clojure,
               :imports [],
               :requires [[datomic.api :as d]],
               :params [db e ref-attr v-id-attr retract-target-entity? val-maps],
               :code (let [v-id-attr (d/ident db v-id-attr)
                           ref-attr (d/ident db ref-attr)
                           ent (d/entity db e)
                           new-ids (into #{} (map v-id-attr) val-maps)]
                       (into
                         [{:db/id e, ref-attr val-maps}]
                         (comp
                           (map v-id-attr)
                           (remove new-ids)
                           (map (fn [id]
                                  (if retract-target-entity?
                                    [:db.fn/retractEntity [v-id-attr id]]
                                    [:db/retract e ref-attr [v-id-attr id]])
                                  )))
                         (get ent ref-attr))
                       )}
 }