attribute-invariant-pipeline.clj

(def multi-transfer-invariant
  '[$balance-sums
    [:find [(sum ?balance-before) :as sum-before
            (sum ?balance-after)  :as sum-after
            (sum ?balance-change) :as sum-of-change]
     :with ?affected-entity
     :in $before $after $txn
     :where
     ;; Unify data from databases and transactions with affected-entity
     [$after    ?affected-entity         :account/balance    ?balance-after]
     [$txn      ?affected-entity         :account/balance    ?balance-change]
     [(get-else $before ?affected-entity :account/balance 0) ?balance-before]

     ;; 1. Zero-Sum
     [(+ ?balance-change ?balance-before) ?computed-balance-after]
     [(= ?balance-after ?computed-balance-after)]

     ;; 2. Positivity
     [(>= ?balance-after 0)]

     ;; 3. Sender spending
     [$txn _ :transaction/signed-by ?sender]
     (or
       ;; sender balance should only decrease
        (and [(= ?sender ?affected-entity)]
             [(> ?balance-before ?balance-after)])
       ;; recipient balances should only increase
        (and [(not= ?sender ?affected-entity)]
             [(< ?balance-before ?balance-after)]))]

    $balance-check
    [:find ?matches .
     ;-- this statement:
     :within $balance-sums
     ;-- gets rewritten as:
     :in [?sum-before ?sum-after ?sum-of-change]
     ;--
     :where [(= ?sum-before ?sum-after)]
            [(= ?sum-change 0) ?matches]]])


;;; Schema

{:db/ident :datopia.ednt/balance
 :db/cardinality :db.cardinality/one
 :db/valueType :db.type/bigdec
 :db/invariant multi-transfer-invariant}


;;; Balance transfer Usage

(d/q multi-transfer-invariant
  ;; current state
  @conn
  ;; apply transaction to current state
  (dc/db-with @conn transfer-transaction)
  ;; empty database with only transaction applied
  (dc/db-with (dc/empty-db schema) transfer-transaction)
  transfer-transaction)

query-pipeline-syntax.clj

(def vote-results-query
  '[$votes
    [:find ?issue, ?proposal-name, (count ?vote) :as vote-count
     :in $ ?issue
     :where
     [?ballot   :ballot/issue ?issue]
     ;; Bind the proposal
     [?proposal :proposal/name ?proposal-name]
     ;; Count only votes for this Ballot
     [?vote     :voter/ballot ?ballot]
     ;; Bind the votes for this proposal
     [?vote     :voter/vote-on-proposal ?proposal]]

    $most-voted
    [:find (max ?vote-count) :as winning-vote-count .
     ;-- this statement:
     :within $votes
     ;-- gets rewritten as:
     :in [[?issue ?proposal-name ?vote-count]]]
     ;--

    $winners
    [:find ?proposal-name ?vote-count
     ;-- this statement:
     :within $votes $most-voted
     ;-- gets rewritten as:
     :in [[?issue ?proposal-name ?vote-count]] ?winning-vote-count
     ;--
     :where [(= ?winning-vote-count ?vote-count)]]])