Datascript101 - Chapter 2

Datascript101-Chapter2.clj

(ns dt.core
  (:require [datascript.core :as d]))

;; schema so nice
(def schema {:maker/email {:db/unique :db.unique/identity}

             :car/model {:db/unique :db.unique/identity}
             :car/maker {:db/type :db.type/ref}
             :car/colors {:db/cardinality :db.cardinality/many}})

;; create the connection
(def conn (d/create-conn schema))

;; insert a car
(d/transact! conn [{:maker/email "ceo@bmw.com"
                    :maker/name "BMW"}
                   {:car/model "E39530i"
                    :car/maker [:maker/email "ceo@bmw.com"]
                    :car/name "2003 530i"}])

;; insert a car by using a lookup ref to an already existing maker
(d/transact! conn [{:car/model "E39520i"
                    :car/maker [:maker/email "ceo@bmw.com"]
                    :car/name "2003 520i"}])

;; Query all cars made by our maker
(d/q '[:find [?name ...]
       :where
       [?c :car/maker [:maker/email "ceo@bmw.com"]]
       [?c :car/name ?name]]
     @conn)


;; query some stuffs
(d/entity @conn [:car/model "E39530i"]) ;; {:db/id 2}

(d/entity @conn [:maker/email "ceo@bmw.com"]) ;; {:db/id 1}

;; lazy-query an attribute out of an entity
(:maker/name (d/entity @conn [:maker/email "ceo@bmw.com"])) ;; "BMW"

;; Update the name of a maker by using lookup refs
(d/transact! conn [{:maker/email "ceo@bmw.com"
                    :maker/name "BWM Motors"}])

;; query the name again and see it change
(:maker/name (d/entity @conn [:maker/email "ceo@bmw.com"])) ;; "BMW Motors"