invariant + Datahike Example

datahike_scratch.clj

(ns invariant.datahike-scratch
  (:refer-clojure :exclude [+])
  (:require [invariant.datahike
             :refer [+]]
            [datahike.api  :as d]
            [datahike.core :as dc]))

(defn query [q conn tx]
  (d/q q
       @conn
       (dc/db-with @conn tx)
       (dc/db-with (dc/empty-db) tx)
       tx))

(let [uri    "datahike:mem:///invariant-test"
      schema [#:db{:ident       :x64.lcoin/balance
                   :valueType   :db.type/bigdec
                   :cardinality :db.cardinality/one}
              #:db{:ident       :transaction/signed-by
                   :valueType   :db.type/long
                   :cardinality :db.cardinality/many}]]
  (d/delete-database uri)
  (d/create-database uri)
  (let [conn (d/connect uri)]
    (d/transact conn schema)
    (d/transact conn [{:db/id             1
                       :x64.lcoin/balance 1M}
                      {:db/id             2
                       :x64.lcoin/balance 0M}
                      {:db/id             3
                       :x64.lcoin/balance 3000M}
                      {:db/id 4}])
    (let [q '[:find ?sum-change .
              :in   $before $after $empty+tx $tx
              :where
              [(subquery [:find (sum ?balance-change) .
                          :with ?entity
                          :in   $before $after $empty+tx _
                          :where
                          [$empty+tx ?entity :x64.lcoin/balance _]

                          [$after ?entity :x64.lcoin/balance ?balance-after]
                          [(>= ?balance-after 0M)]

                          [(get-else $before ?entity :x64.lcoin/balance 0M) ?balance-before]
                          [(- ?balance-after ?balance-before) ?balance-change]

                          [$empty+tx _ :transaction/signed-by ?sender]
                          [(= ?sender ?entity) ?is-sender]
                          [(>= ?balance-change 0M) ?pos-change]
                          [(or ?is-sender ?pos-change)]]
                         $before $after $empty+tx $tx) ?sum-change]
              [(zero? ?sum-change)]]
          txn [[:db.fn/call + 1 :x64.lcoin/balance -1M]
               [:db.fn/call + 2 :x64.lcoin/balance +1M]
               [:db/add 1 :transaction/signed-by 1]]]
      (query q conn (concat schema txn)))))