AE
Ash Elixir•2y ago
Rebecca Le

Broadcasting pubsub update notifications only if the resource has been changed?

At the moment a broadcast is made after the action is successfully performed - even if nothing on the record actually changed. My scenario is having a background worker that checks validity of some credentials in a loop periodically, in an action like so: 
    update :update_credential_validity do
      change set_attribute(:invalid, true)
      change set_attribute(:invalid, false), where: [{Vendor.CredentialValidation, []}]
    end
    update :update_credential_validity do
      change set_attribute(:invalid, true)
      change set_attribute(:invalid, false), where: [{Vendor.CredentialValidation, []}]
    end
A resource with valid credentials will have invalid: false and that attribute won't change, but I still get a pubsub notification after each check. It's not causing any real problems, but a) the logs are super noisy with all the extra unnecessary pubsub notifications being sent around, and b) unnecessary work is being done by the recipients of the broadcast that doesn't need to be. (eg. templates might re-render, or in my case the background worker presence is verified, and started if its not already). Is there some way we could configure pubsub for updates to not broadcast unless something was actually updated?
6 Replies
ZachDaniel
ZachDaniel•2y ago
Hmm...I'm wondering if perhaps that should be the default behavior. We won't always be able to know, i.e for atomic operations though. So perhaps it should be action by action configuration
Rebecca Le
Rebecca LeOP•2y ago
it seems like a sensible default to me, but it would definitely be a breaking change if anyone was relying on the old behaviour. i can't think of an example of when the current behaviour would be wanted though. for atomic operations (or any case where it can't be known if something happened or not) we should probably default to sending the notification
ZachDaniel
ZachDaniel•2y ago
Yeah, agreed. Which we should be able to do 👍 Come to think of it though, I think people probably are relying on this i.e with an action like add_comment they are likely relying on getting the parent notification. You could monitor for a comment created, or for the add_comment action being called. So I think we're going to have to do this slightly differently. We could put it in the action: 
update :update do
  notify_with_no_changes? true
end
update :update do
  notify_with_no_changes? true
end
or in the pub sub notifier 
update :action, "foo:bar" do
  only_when_changed? true
end
update :action, "foo:bar" do
  only_when_changed? true
end
thoughts?
Rebecca Le
Rebecca LeOP•2y ago
ah right, if you had an update action that doesn't touch the resource itself, but uses hooks to do related stuff, you still want to know about it. that makes sense I think configuring it in the notifier would be better
ZachDaniel
ZachDaniel•2y ago
Agreed. Could you open an issue in Ash? I’ll see if I can add it this week 🙂
Rebecca Le
Rebecca LeOP•2y ago
issue created https://github.com/ash-project/ash/issues/647 so I'll close this thread
GitHub
proposal: Allow configuring pubsub notifiers for update actions to ...
Is your feature request related to a problem? Please describe. (See https://ash-hq.org/forum/support/1126780995845230632 for some context) At the moment, pubsub notifiers will always broadcast noti...

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