subscribing for a side-effect?

[keturn]

Hi, I've been experimenting with Cami, and it's going pretty well so far.

I started using query to fetch a resource, and I'm trying to separate some functionality that happens in response to that.

One component displays the resource as-is. That's working fine.

I want to be able to have a second object that, when it notices that Foo resource is available, processes it to come up with a new Foobar.

It feels like this should be basically

this.foo = this.query(…)
this.foo.onValue(result => processFooIntoFoobar(result.data))

but there's some nuance that I'm missing. That callback seems to only be getting the new value in its pending status, not when it is finished with the data.

[kennyfrc]

Hi @keturn! Glad to hear you're liking it so far.

The short answer on why query and onValue don't work together is that query returns an ObservableState (similar to signals in preact / solid) and onValue expects an ObservableStream (similar to RXJS streams / Bacon.js), so there are actually two paradigms within cami.

There are two possible ways to accomplish what you want to do:

• The "signals" way: query + effect (see here: this.effect)
• The "streams" way: http + onValue (see here: http stream)

The way you can distinguish the difference between the two is as follows:

• effect listens to changes in a state (singular, non time-based)
• onValue listens to many state emissions over time (plural, time-based)

Since query just modifies a state, onValue only got the original state emission, and was not aware of the state change that happened later. http is designed to emit many states over time.

Some jsfiddle examples:

• Subscribing to query's return value outside of the template by using effect: link
• Subscribing to http by using onValue: link

Lastly, you can also do this pipeline if desired: http -> onValue -> state, similar to what Ryan Carniato described here: link (in that comment, you can replace 'Flyd' with http / onValue and 'Solid State Object' with query / effect / state.

[kennyfrc]

Although fwiw, I usually do query then store.dispatch for those type of things. I don't use effect typically.

I also rarely use stream and http -- it's most useful for real time event streams