Utility functions for bridging Datomic/Datascript

util.cljx

(ns allgress.datascript.util
  (:require [clojure.walk :refer [postwalk]]))

;;; Datomic pull API will return :db/idents as references, like {:my-enum-att {:db/ident :enum-value}}. 
;;; This function replaces with the Datascript equivalent {:my-enum-att :enum-value}. Only works 
;;; for true "enums", whose only attribute in the entity map is :db/ident.
defn replace-enum-refs [entity-map]
  (postwalk
    (fn [arg]
      (if (and (coll? arg) (map? (second arg)) (= 1 (count (second arg))) (contains? (second arg) :db/ident))
        (do
          [(first arg) (:db/ident (second arg))])
        arg))
    entity-map))

;;; To pull enums using Datomic pull API, you would specify a pattern like [{:my-enum-att [:db/ident]}]. 
;;; For Datascript, you only need to specify the attribute: [:my-enum-att]. This function transforms the
;;; Datomic form to the Datascript form.
(defn replace-enum-patterns [entity-pattern]
  (postwalk
    (fn [arg]
      (if (and (map? arg) (= [:db/ident] (first (vals arg))))
        (first (keys arg))
        arg))
    entity-pattern))

;;; Utility function for creating UUID in either Clojure or ClojureScript.
(defn random-uuid []
  #+clj (java.util.UUID/randomUUID) #+cljs (datascript/squuid))

;;; Extends UUID in ClojureScript to implement IComparable, so Datomic attributes of type db.type/uuid 
;;; can be added to Datascript.
#+cljs
(extend-type UUID
  IComparable
  (-compare [x y] (compare (datascript/squuid-time-millis x) (datascript/squuid-time-millis y))))