[JAVA] The world of clara-rules (5)

Last time

If you use the accumulator function of clara-rules, you can realize something like an aggregate function in sql, so try it this time. I will see it.


--Use the one in the clara.rules.accumulators namespace --Min / max / sum etc. are provided by default --You can also create your own accumulator (accum function) --Can be used in defquery on the left side of defrule


[<variable name to bind> <-<accumulator>: from [<fact> + <constraint>]]

Try to move

I tried the following code.

(ns clara-rules.accumulator
  (:require [clara.rules :refer [fire-rules insert mk-session query defquery]]
            [clara.rules.accumulators :as acc]))

(defrecord SomeAmount [id amt])

(defquery test-query
  [?largest-amt <- (acc/max :amt) :from [SomeAmount]]
  [?total <- (acc/sum :amt) :from [SomeAmount]]
  [?grouped <- (acc/grouping-by :id) :from [SomeAmount]]
  ;;Total by groups
   <- (acc/grouping-by :id (fn [m]
                             ;;Accepts map key=field for grouping
                             ;;value=seq of maps of records that were grouped
                             (map (fn [[k seq-of-records]]
                                    {k (reduce + (map :amt seq-of-records))})
   :from [SomeAmount]])

(-> (mk-session)
    (insert (->SomeAmount :a 4)
            (->SomeAmount :a 8)
            (->SomeAmount :b 32)
            (->SomeAmount :b 21)
            (->SomeAmount :c 1)
            (->SomeAmount :c 9))
    (query test-query))
;; => ({:?largest-amt 32,
;;      :?total 75,
;;      :?grouped {:a [#clara_rules.accumulator.SomeAmount{:id :a, :amt 4}
;;                     #clara_rules.accumulator.SomeAmount{:id :a, :amt 8}],
;;                 :b [#clara_rules.accumulator.SomeAmount{:id :b, :amt 32}
;;                     #clara_rules.accumulator.SomeAmount{:id :b, :amt 21}],
;;                 :c [#clara_rules.accumulator.SomeAmount{:id :c, :amt 1}
;;                     #clara_rules.accumulator.SomeAmount{:id :c, :amt 9}]},
;;      :?grouped-and-summed ({:a 12} {:b 53} {:c 10})})

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