Brief excision example

;com.datomic/peer {:mvn/version "1.0.7075"} see: https://docs.datomic.com/accessing/integrating-peer-lib.html and peer docs: https://docs.datomic.com/clojure/index.html
(ns jaretbinford.excision
  (:gen-class)
    (:require [datomic.api :as d]))

; Start a dev transactor `bin/transactor config/samples/dev-transactor-template.properties` see: https://docs.datomic.com/setup/pro-setup.html
; Use backup and restore to make a dev database of the Mbrainz sample. Or transact your own schema and data on your test system. See:https://github.com/Datomic/mbrainz-sample
; bin/datomic restore-db file:///Users/jaret.binford/Jaret/releases/pro/backups/mbrainz-1968-1973 datomic:dev://localhost:4334/mbrainz-1968-1973

(d/get-database-names "datomic:dev://localhost:4334/*" )
(def db-uri "datomic:dev://localhost:4334/mbrainz-1968-1973")
(def conn (d/connect db-uri))
(def db (d/db conn))

;A pull on my John Lennon entity, 527765581346058 to see what attributes the entity has
(d/pull db '[*] 527765581346058)
;=>
;{:artist/sortName "Lennon, John",
; :artist/name "John Lennon",
; :artist/type #:db{:id 17592186045423},
; :artist/country #:db{:id 17592186045580},
; :artist/gid #uuid"4d5447d7-c61c-4120-ba1b-d7f471d385b9",
; :artist/startDay 9,
; :artist/endDay 8,
; :artist/startYear 1940,
; :artist/endMonth 12,
; :artist/endYear 1980,
; :db/id 527765581346058,
; :artist/startMonth 10,
; :artist/gender #:db{:id 17592186045420}}

;Excise John Lennon's attribute name from the John Lennon entity:
@(d/transact conn [{:db/excise 527765581346058
                    :db.excise/attrs [:artist/name]}])
;=>
;{:db-before datomic.db.Db,
; @abe6d57e :db-after,
; datomic.db.Db @35f69a7d,
; :tx-data [#datom[13194139681660 50 #inst"2024-05-25T11:54:17.594-00:00" 13194139681660 true]
;           #datom[17592186192765 15 527765581346058 13194139681660 true]
;           #datom[17592186192765 16 67 13194139681660 true]],
; :tempids {-9223300668110598143 17592186192765}}

; Note excision will not happen immediately: https://docs.datomic.com/operation/excision.html#how-it-works but you can track excision with https://docs.datomic.com/operation/excision.html#tracking-excisions
(d/q '[:find ?e
       :in $ ?e
       :where [_ :db/excise ?e]]
     (d/db conn)
     527765581346058)
;=> #{}

; After running the excision I will request index and sync:
(d/request-index conn)

;Once indexing completes and I grab a new db:
(d/q '[:find ?e
       :in $ ?e
       :where [_ :db/excise ?e]]
     (d/db conn)
     527765581346058)
;=> #{[527765581346058]}

;;In the logs you will see:
;│2024-05-25 07:54:17.614 INFO  default    datomic.update - {:event :update/create-index, :next-t 148350, :id "mbrainz-1968-1973-392b18a1-7301-4a88-bee1-369ae05f3a98", :phase :begin, :pid 67684, :tid 25}                                                                                                                                                                      │
;│2024-05-25 07:54:17.624 INFO  default    datomic.index - {:event :excise/ents, :next-t 148350, :count 1, :pid 67684, :tid 25}
;Your process monitor will also report: :ExciseSegments {:lo 0, :hi 1, :sum 4, :count 8}