Om Next FAQ

How can I implement optimistic commits?

How can I delay loads?

How do I communicate with the server?

Provide a function to the :send key of the reconciler's parameter map (along with :state and :parser). This will be a function which takes two parameters: the EDN of the query expression fragment that will be passed to the server, and a callback to handle the response. Om will provide the callback, your function just needs to make the request and ensure that the callback receives, as its one argument, data in the format of an EDN result of a query expression -- for example by simply reading a transit-json response from the server back into EDN. Example:

(defn transit-post [url]
  (fn [{:keys [remote]} cb]
    (.send XhrIo url
      (fn [e]
        (this-as this
          (cb (t/read (t/reader :json) (.getResponseText this)))))
      "POST" (t/write (t/writer :json) remote)
      #js {"Content-Type" "application/transit+json"})))

Why is my component not rerendered after calling transact!?

The transact! function takes an initiating component and a query expression that consists of mutations and any number of reads. The first question to ask yourself is: does the transaction affect keys that are not part of the initiating component's query? Om implicitly updates the initiating component from the local app state after the transaction but if any keys outside the component are affected, they need to be added to the transact! query expression explicitly. An example: component Foohas a query[:foo/bar :foo/baz]and performs the transaction(om/transact this [(app/do-something)]). If mutate 'app/do-something changes :foo/bar or :foo/baz, the component will be rerendered with the new data after the transaction. If it changes:something/else however, the code has to be changed to (om/transact this [(app/do-something) :something/else])`.