Is it ok to reference subscriptions in another subscription? I can't see any conceptual reason why not but better safe than sorry...
On 27 March 2015 at 21:15, Mike Thompson <[email protected]> wrote: > On Saturday, March 28, 2015 at 7:52:13 AM UTC+11, Colin Yates wrote: >> Hi Mike, yep, that is what I meant by "> I can work around this - the >> subscription code typically delegates to a 'plain' defn so I can >> retrieve the data from the db and call the same defn, but sometimes >> that jars a bit." :). >> >> >> On 27 March 2015 at 20:47, Mike Thompson <[email protected]> wrote: >> > On Saturday, March 28, 2015 at 7:36:26 AM UTC+11, Colin Yates wrote: >> >> I have various chunks of reference data, say a tree or a list of _all_ >> >> (i.e. active and historical) entities. I then have various subscriptions >> >> which refine that view, for example: >> >> - only active >> >> - only active but including a given id >> >> >> >> In the handler I sometimes need access to this data, but according to the >> >> re-frame doc: >> >> >> >> "Rules: >> >> >> >> components never source data directly from app-db, and instead, they use >> >> a subscription. >> >> subscriptions are only ever used by components (they are never used in, >> >> say, event handlers)." >> >> >> >> I can work around this - the subscription code typically delegates to a >> >> 'plain' defn so I can retrieve the data from the db and call the same >> >> defn, but sometimes that jars a bit. >> >> >> >> The fact it is useful for me to do something not only discouraged but >> >> actively against the rules makes me question my design somewhat; what is >> >> the rationale for not allowing an event handler to view a subscription? >> >> Am I wrong in viewing a subscription as merely a view on the data in >> >> which case I don't see the danger... >> >> >> >> I get that components should be divorced from the structure of the DB and >> >> event handlers necessarily need to know the structure but I see a >> >> subscriptions as more than just structure - it sometimes applies >> >> transformations that I would want to re-use. > > I'll expand ... > > Think about a subscription handler as: > 1. A query function (db) -> val ... > 2. some reaction wrapping around the outside > > The reaction wrapping is very useful for when you need "a stream" of updates > over time. Components need to get a told when "app-db" changes. > > But event handlers don't need a stream. They need a one-off value, based off > the db param they have been supplied. > > If you do try to use a subscription in an event handler, you'll get a memory > leak. The reaction won't get properly "disposed" (it is automatically done > for you when a Signal chain feeds through into a component). > > So, repeating myself: event handlers don't need a constant stream of > updates. They don't need a subscription. All they need to do is call a > function on "db" to get a value, so factor that function out of the > subscription and make it available. > > -- > Mike > > > > -- > Note that posts from new members are moderated - please be patient with your > first post. > --- > You received this message because you are subscribed to the Google Groups > "ClojureScript" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/clojurescript. -- Note that posts from new members are moderated - please be patient with your first post. --- You received this message because you are subscribed to the Google Groups "ClojureScript" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/clojurescript.
