Pointers to why invoking the following handler causes the ratom to emit null?

(register-handler
  :load-data
  (fn [db _]
   (js/console.warn "Loading data..")
   (-> (js/fetch "")
       (.then #(.json %))
       (.then (fn [data] (mapv #(.-url %) data)))
       (.then #(dispatch [:process-data %])))))

you’re not returning db

The thing is, the contents in the db doesn't change

Just the null gets emitted causing a crash

yeah, but this handler returns the promise

and this sets the db to the promise

you should return the unchanged db anyway

Oh, didn't know that

(register-handler
  :load-data
  (fn [db _]
   (js/console.warn "Loading data..")
   (-> (js/fetch "")
       (.then #(.json %))
       (.then (fn [data] (mapv #(.-url %) data)))
       (.then #(dispatch [:process-data %])))
   db))

May I ask how re-frame knows which db to work upon?

Because I don't see

;; initial state of app-db
(def app-db {:greeting "Hello Clojure in iOS and Android!" :data (mapv str (range 1 100))})

there is a dispatch in the core (if you’re using the template)

(register-handler
 :initialize-db
 validate-schema-mw
 (fn [_ _]
   app-db))

Yes, I'm using the template

So the first thing it gets is the db?

this does the magic, as it returns the app-db

yeah

Oh thank you, stuck for days because of this

if you want to reset the db to the default values, you can dispatch :initialize-db anytime

Great!

Does it specifically have some associating with the :initialize-db key?

Or the first thing returned to be exact?

Yes, the null is gone! 😄

nothing related to :initialize-db. it’s just the first event processed, and its handler always return the default db

Awesome

take a look in init inside core.cljs. there should be a line like this: (dispatch-sync [:initialize-db])

Certainly, I really appreciate the response, I hope this is documented and that I missed to read the section

idk if it’s documented as it’s more of a pattern present in the template, rather than some re-frame characteristic

Yes, I noticed that line but didn't know it was required for the db to be returned

@debug, When you dispatch with a key, that adds your dispatch-vector the event-queue, which uses the first item in the dispatch-vector (`:initialize-db`) to lookup what handler function to use.

I meant that the documentation regarding that db must be returned by the handler

oh, yeah, that’s documented 😆

https://github.com/Day8/re-frame#event-handlers

Next the handler function for your dispatch vector is used to swap the current value of the db

Yeah there's a lot of docs about this 😄

I read that a few times and still I missed, a fun reading btw 🙂

@debug: look what i found in re-frame’s wiki: https://github.com/Day8/re-frame/wiki/Bootstrap-An-Application#the-right-data

their wiki is incredibly useful, I’ve never took the time to read it

There’s gold in that wiki