Support subscribing to subscriptions

[valerauko]

re-frame supports multiple layers of subscriptions and it only recomputes what's necessary. cf https://day8.github.io/re-frame/subscriptions/#why-layer-2-extractors

How difficult do you think this could be to port to re-dash?

[wkok]

Hello!

re-dash subscriptions internally uses ClojureDart Cells to watch for changes to a specific key in app-db, which similar to re-frame would only result in recomputing the view if the value subscribed to actually changed.

For example, given an app-db of

{:name1 "Jack"
 :name2 "Jill"}

and the view subscribes to both names individually:

(m/Column
   .children
   [(f/widget
      :watch [name1 (rd/subscribe [::model/get-name1])]
      (m/Text name1))
    (f/widget
      :watch [name2 (rd/subscribe [::model/get-name2])]
      (m/Text name2))])

then say only :name1 is later changed from anywhere, we can be sure that the widget tree for :name2 won't be recomputed

Is there something more that multi layer subscriptions gives that I may be missing?

[wkok]

Ahh the link you shared refered to layer 2 extractors, but I think you're referring to layer 3 materialised view mentioned here
https://day8.github.io/re-frame/subscriptions/#the-four-layers

That requires some thinking, but yes, it would be nice to support

[valerauko]

Sorry, I meant to link to the layer 3 materialised view part...

In re-frame these "input functions" subscribe to other subscriptions. Is such a thing possible with cljd cells?

[wkok]

Yes, according to the ClojureDart cheatsheat cells can have other cells as their dependencies.

I'll experiment with it a bit in the next couple days

[wkok]

Promising news, in the layer-3-materialised-view branch it works now where a subscription can subscribe to one other subscription (single signal) via the signals function

Not yet implemented is to support a vector or a map of signals, but at the moment this works:

  ;; Layer 2 - Extractor
  (rd/reg-sub
    ::get-count
    (fn [db _query-vec]
      (:current-count db 0)))


  ;; Layer 3 - Materialised View
  (rd/reg-sub
    ::get-count-description

    ;; signals function
    (fn [query-v]
      (rd/subscribe [::get-count query-v]))

    ;; computation function
    (fn [get-count _query-v]
      (str "The count is exactly " get-count)))

[valerauko]

Awesome! If you'd rather, I can help from there and implement the rest of the feature?

[wkok]

I've just pushed a commit to this branch that adds support for a vector or map of signals