hi all

I have what is probably a very stupid question - how does a subscription know its value has changed?

using random example from re-frame docs I have open, say I write:

(re-frame/reg-event-db
  :set-active-panel
  (fn [db [_ value]]
    (assoc db :active-panel value)))

(re-frame/reg-sub
  :active-panel
  (fn [db _]
    (:active-panel db)))

when I then do a (re-frame/dispatch [:set-active-panel :panel1]), how does re-frame know that whatever is subscribing to :active-panel needs to be refreshed?

right now I'm dealing with a situation like this: I have subscriptions A and B, and then a subscription C that uses A and B as input vectors, and just concatenates them) my component subscribes to C, and there are input fields that trigger calls which change (via an event-db dispatch) values that are listened to by A and B

somehow, C does not catch the fact that values in DB are changed, and in trying to figure that out I realize I can't find any info on how do subscriptions actually know what's going on

moreover, looking at the app state via re-frisk, I discovered that even A and B don't notice changes in the DB

re-frame-10x is a tool which provides more information on when subscriptions are run and what values they create.

You generally don't need to know how it works

BTW, if the new value A tests = to the old value of A then no change is propogated

@temporal.pl ^^^

thanks

I just fixed the problem, turns out it was PEBKAC (like usual), a mistake with qualified/unqualified keys

careful looking at re-frisk window helped

still, knowing how this works under the hood would help me keep some peace of mind 🙂

for instance, I have some subscriptions I inherited in the codebase that look like (or (get-in app-db [:foo :bar]) (some-default-computed-value)), and yet they update themselves if the db state under :foo :bar changes

does re-frame recompute all subscriptions at any db change?

I'd encourage you to read the docs: https://github.com/Day8/re-frame/blob/master/docs/SubscriptionInfographic.md

re-reading the flowchart now, thanks

Also read the link at the bottom of that page, to the todomvc example. It is heavily commented.

ok, thanks

I think the answer to my question is actually on "The Signal Graph - a four layer tree" part of the flowchart, where there's a note that data flow stops when a subscription returns unchanged value

I believe this resolves my confusion

Righto. Keep re-frame-10x in mind too

I will!

related to this question (https://clojurians.slack.com/archives/C073DKH9P/p1539431269000200) which I maybe asked at the wrong time/day

I got something vaguely working but I'm not sure it makes so much sense, and strangely I can't really find anything online about that

anyone doing that who would like to share how they do oauth2 authentication in general? (Maybe it's more a SPA question more than a re-frame problem specifically)

@andrea.crotti did you read this doc? https://github.com/Day8/re-frame/blob/master/docs/SubscriptionFlow.md

@temporal.pl you might also be interested ^^^ vvv

Be sure to read through all the docs. https://github.com/Day8/re-frame/tree/master/docs