Autorefresh as pubsub

28.12.2021, 18:07

I set up a websocket connection using this example https://ihp.digitallyinduced.com/Guide/websockets.html

Would it be possible to track certain DB tables here as well? Like AutoRefresh is doing for actions. I want to push something over WS when a table is updates/inserted. I understand that is what autorefresh is doing, but i'm trying to use this as a backend to backend communication, and autorefresh seems to require an action

Lillo PRO

28.12.2021, 18:12

Maybe DataSync could be for you? https://ihp.digitallyinduced.com/Guide/realtime-spas.html

It lets you subscribe to certain database tables like for example this through JavaScript:

function callback(todos) {
    console.log('todos did change', todos);
}

const todos = await query('todos').fetchAndRefresh(callback);

Aksel Stadler Kjetså

28.12.2021, 18:13

Thanks! I'll check it out :) will update if i make it work!

Aksel Stadler Kjetså

28.12.2021, 18:18

Interestingly the documentations shows how to listen for changes from javascript, but not how to do it from within Haskell. So it is definitely possible, i just need to find the haskell side code of the ws connection

marc PRO

28.12.2021, 18:26

You can find the DB watcher code for DataSync starting here: https://github.com/digitallyinduced/ihp/blob/master/IHP/DataSync/Controller.hs#L76

You need to do two things:

Set up a notification trigger, e.g. like here https://github.com/digitallyinduced/ihp/blob/master/IHP/DataSync/Controller.hs#L77
Get a pgListener instance from the application context and then call subscribe or subscribeJSON (this automatically decodes the response the postgres event as json). https://github.com/digitallyinduced/ihp/blob/master/IHP/DataSync/Controller.hs#L114

AutoRefresh also uses the PGListener API.

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