Om.next: reading joins and unions while preserving remotes

reading-joins-and-unions-preserving-remotes.clj

;; Attribution note: this was taken from @petterik on Slack on 2017-05-02

;; Here are two functions I use for reading nested queries, joins and unions.

(defn read-join [{:keys [parser query target ast] :as env}]
  (let [ret (parser env query target)]
    (if target
      (when (seq ret)
        {target (assoc ast :query ret)})
      {:value ret})))

(defn read-union [{:keys [query] :as env} union-key]
  (let [union-query (cond-> query (map? query) (get union-key))]
    (read-join (assoc env :query union-query))))

;; Here's what the implementation of your reads would be with them

(defmethod app-read :router-data [{:keys [query parser] :as env} k p]
  (read-join env))

(defmethod app-read :route/data  [{:keys [state query parser] :as env} k p]
  (let [st @state
        route (get st :app/route)]
    (read-union env route)))

;; Since joining child component's queries is so common, I've special cased
;; keys starting with "join", e.g. {:join/child (om/get-query Child)}

(defmethod app-read :default
  [env k p]
  (= "join" (namespace k))
  (read-join env))