Using database functions in Datomic transactions and annotating transaction history

accounts.clj

(use '[datomic.api :only [q db] :as d])

(def uri "datomic:mem://accounts")

;; create database
(d/create-database uri)

;; connect to database
(def conn (d/connect uri))

;; parse schema dtm file
(def schema-tx (read-string (slurp "db/schema.dtm")))

;; submit schema transaction
@(d/transact conn schema-tx)

;; parse seed data dtm file
(def data-tx (read-string (slurp "db/accounts.dtm")))

;; submit seed data transaction
@(d/transact conn data-tx)

(defn decorate 
  "Simple function to pull out all the attributes of an entity into a map"
  [id]
  (let [ db (d/db conn)
         e (d/entity db id)]
    (select-keys e (keys e))))

(defn decorate-results 
  "maps through a result set where each item is a single entity and decorates it"
  [r]
  (map #(decorate (first %)) r))

(defn accounts
  "returns all accounts"
  []
  (d/q '[:find ?a :where [?a :account/balance _]] (d/db conn)))

(defn history
  "Returns all transactions"
  ([] (d/q '[:find ?tx :in $ :where [?tx :ot/amount _]] (d/db conn)))
  
  ([acct] (let [rules '[[(party ?t ?a)
                          [?t :ot/from ?a]]
                        [(party ?t ?a)
                         [?t :ot/to ?a ]]]]

                (d/q '[ :find ?t :in $ % ?a :where (party ?t ?a)]
                      (d/db conn) rules acct))))

(defn transfer [ from to amount note]
  (let [txid (datomic.api/tempid :db.part/tx)]
    (d/transact conn [[:transfer from to amount]                      
                      {:db/id txid, :db/doc note :ot/from from :ot/to to :ot/amount amount}])))

(defn credit [ to amount ]
  (d/transact conn [[:credit to amount]]))


(def issuer (ffirst (d/q '[:find ?e :where [?e :account/name "issuer"]] (d/db conn))))
(def bob (ffirst (d/q '[:find ?e :where [?e :account/name "bob"]] (d/db conn))))
(def alice (ffirst (d/q '[:find ?e :where [?e :account/name "alice"]] (d/db conn))))

(transfer issuer alice 77M "Issuance to Alice")
(transfer issuer bob 23M "Issuance to Bob")
(transfer alice bob 7M "Tomatoes")

(prn (decorate-results (accounts)))

(println "All transactions")
(prn (decorate-results (history)))

(println "Issuer's transactions")
(prn (decorate-results (history issuer)))
(prn (decorate issuer))
(println)

(println "Bob's transactions")
(prn (decorate-results (history bob)))
(prn (decorate bob))
(println)

(println "Alice's transactions")
(prn (decorate-results (history alice)))
(prn (decorate alice))
(println)

;; Throws an exception
(transfer alice bob 71M "Tomatoes")

accounts.dtm

[
{:db/id #db/id[:db.part/user -1000001], :account/name "issuer", :account/balance 0M, :account/min-balance -1000M}
{:db/id #db/id[:db.part/user -1000002], :account/name "bob", :account/balance 0M, :account/min-balance 0M}
{:db/id #db/id[:db.part/user -1000003], :account/name "alice", :account/balance 0M, :account/min-balance 0M}
]

schema.dtm

[
  ;; accounts

  { :db/id #db/id[:db.part/db]
    :db/ident :account/name
    :db/valueType :db.type/string
    :db/cardinality :db.cardinality/one
    :db/fulltext true
    :db/unique :db.unique/value
    :db/doc "An account's name"
    :db.install/_attribute :db.part/db}

  { :db/id #db/id[:db.part/db]
    :db/ident :account/balance
    :db/cardinality :db.cardinality/one
    :db/valueType :db.type/bigdec
    :db/doc "The accounts balance"
    :db.install/_attribute :db.part/db}

  { :db/id #db/id[:db.part/db]
    :db/ident :account/min-balance
    :db/cardinality :db.cardinality/one
    :db/valueType :db.type/bigdec
    :db/doc "The accounts maximum balance"
    :db.install/_attribute :db.part/db}

  { :db/id #db/id[:db.part/db]
    :db/ident :ot/amount
    :db/valueType :db.type/bigdec
    :db/cardinality :db.cardinality/one
    :db/doc "Amount transacted"
    :db.install/_attribute :db.part/db}

  { :db/id #db/id[:db.part/db]
    :db/ident :ot/from
    :db/valueType :db.type/ref
    :db/cardinality :db.cardinality/one
    :db/doc "Transferee"
    :db.install/_attribute :db.part/db}

  { :db/id #db/id[:db.part/db]
    :db/ident :ot/to
    :db/valueType :db.type/ref
    :db/cardinality :db.cardinality/one
    :db/doc "Recipient"
    :db.install/_attribute :db.part/db}

  { :db/id #db/id [:db.part/user]
    :db/ident :credit
    :db/fn #db/fn { :lang "clojure"
                    :params [db id amount]
                    :code "(let [ e (datomic.api/entity db id)
                                  min-balance (:account/min-balance e 0)
                                  balance (+ (:account/balance e 0) amount) ] 
                                  (if (>= balance min-balance)
                                    [[:db/add id :account/balance balance ]]
                                    (throw (Exception.  \"Insufficient funds\"))))" }}

  { :db/id #db/id [:db.part/user]
    :db/ident :transfer
    :db/fn #db/fn { :lang "clojure"
                    :params [db from to amount]
                    :code "[[:credit from (- amount)]
                            [:credit to amount]]"}}

 ]