Datascript101-Chapter1.clj

## Datascript101-Chapter1.clj
(ns dt.core
  (:require [datascript.core :as d]))

;; schema so nice
(def schema {: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 maker
(d/transact! conn [{:maker/name "Honda"
                    :maker/country "Japan"}])

;; insert a maker a car along with it, referring back to
(d/transact! conn [{:db/id -1
                    :maker/name "BMW"
                    :maker/country "Germany"}
                   {:car/maker -1
                    :car/name "i525"
                    :car/colors ["red" "green" "blue"]}])

;; query a single the name of the cars we know for maker BMW.
(d/q '[:find ?name
       :where
       [?e :maker/name "BMW"]
       [?c :car/maker ?e]
       [?c :car/name ?name]]
     @conn)

;; Another way of doing this
(let [car-entity (ffirst
                  (d/q '[:find ?c
                         :where
                         [?e :maker/name "BMW"]
                         [?c :car/maker ?e]]
                       @conn))]
  (:car/name (d/entity @conn car-entity)))