Datomic: chaining with to explore a prospective sequence of transactions, fairly dorky schema example

with-bonanza.clj

(ns datomic-manual-tests.with-bonanza
  (:require [datomic.api :as d]))

(def db-uri "datomic:mem://people")
(d/create-database db-uri)
(def conn (d/connect db-uri))

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

@(d/transact conn schema)

(defn all-people [db]
  (d/q '[:find ?e ?name ?age
         :where [?e :person/name ?name]
                [?e :person/name ?age]]
       db))

(def db-with-sally (:db-after (d/with (d/db conn) [{:db/id (d/tempid :db.part/user)
                                         :person/age 40
                                         :person/name "Sally"}])))
(all-people db-with-sally)
; #{[17592186045418 "Sally" "Sally"]} -- one prospective branch

(def db-with-sam (:db-after (d/with (d/db conn) [{:db/id (d/tempid :db.part/user)
                                       :person/age 42
                                       :person/name "Sam"}])))
(all-people db-with-sam)
; #{[17592186045418 "Sam" "Sam"]} -- another prospective branch where Sam
;                                    receives this ent-id instead of Sally

; Chained -- a `with` on a `:db-after` from a `with`
(def db-with-sam-alice (:db-after (d/with db-with-sam [{:db/id (d/tempid :db.part/user)
                                                        :person/age 50 :person/name "Alice"}])))
(all-people db-with-sam-alice)
; #{[17592186045418 "Sam" "Sam"]
;   [17592186045420 "Alice" "Alice"]}

(def remove-sam-db
  (let [sam-ent (d/q '[:find ?e .
                       :where [?e :person/name "Sam"]]
                     db-with-sam-alice)]
    (:db-after (d/with db-with-sam-alice [[:db.fn/retractEntity sam-ent]]))))

(all-people remove-sam-db)
; #{[17592186045420 "Alice" "Alice"]} -- only Alice in next chained with
;                                        due to retration

(all-people (d/history remove-sam-db))
; #{[17592186045418 "Sam" "Sam"] [17592186045420 "Alice" "Alice"]}
; Still have Sam in history, though.