A reusable Om component for keeping local application state in sync with server application state
Clojure
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README.md

om-sync

A reusable synchronization component for Om.

Example

om-sync leverages the new :tx-listen option allowed by om.core/root. For example you can imagine setting up your application like so:

(let [tx-chan (chan)
      tx-pub-chan (async/pub tx-chan (fn [_] :txs))]
  (om-sync.util/edn-xhr
    {:method :get
     :url "/init"
     :on-complete
     (fn [res]
       (reset! app-state res)
       (om/root app-view app-state
         {:target (gdom/getElement "app")
          :shared {:tx-chan tx-pub-chan}
          :tx-listen
          (fn [tx-data root-cursor]
            (put! tx-chan [tx-data root-cursor]))}))}))

We publish a transaction queue channel :tx-chan as a global service via :shared so that om-sync instances can listen in.

We can now take any application data and wrap it in an om-sync instance. Whenever application data changes om-sync will synchronize those changes via EDN requests to a server.

Notice in the following that om-sync can take an :on-error handler. This error handler will be given tx-data which contains enough information to roll back the entire application state if something goes wrong.

(defn app-view [app owner]
  (reify
    om/IWillUpdate
    (will-update [_ next-props next-state]
      (when (:err-msg next-state)
        (js/setTimeout #(om/set-state! owner :err-msg nil) 5000)))
    om/IRenderState
    (render-state [_ {:keys [err-msg]}]
      (dom/div nil
        (om/build om-sync (:items app)
          {:opts {:view items-view
                  :filter (comp #{:create :update :delete} tx-tag)
                  :id-key :some/id
                  :on-success (fn [res tx-data] (println res))
                  :on-error
                  (fn [err tx-data]
                    (reset! app-state (:old-state tx-data))
                    (om/set-state! owner :err-msg
                      "Ooops! Sorry something went wrong try again later."))}})
         (when err-msg
           (dom/div nil err-msg))))))

om.core/transact! and om.core/update! now support tagging transactions with a keyword or a vector that starts with a keyword. om-sync listens in on transactions labeled :create, :update, and :delete.

(defn foo [some-data owner]
  (om.core/transact! some-data :foo (fn [_] :bar) :update))

If you are given some component that does not tag its transactions or the tags do not correspond to :create, :update, and :delete you can provide a :tag-fn via :opts to om-sync so that you can classify the transaction yourself.

Contributions

Pull requests welcome.

License

Copyright © 2014 David Nolen

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.