Great - thanks Jamie (and Mike for the FAQ). On 27 March 2015 at 22:37, Jamie Orchard-Hays <[email protected]> wrote: > Subscribing to subscriptions is very useful and works great. > > > On Mar 27, 2015, at 6:19 PM, Colin Yates <[email protected]> wrote: > >> 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. > > -- > 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.
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