Hacker News Reader

Comment by twelve40 | Hacker News Reader

I guess this is like a lower-level version of Parse (on a different, transactional stack too). Pretty cool. I wonder though, often times I have cases that are mostly CRUD but with a little extra: e.g., "create this object and kick off a Stripe payment", or "create this object and send an MQ message". With Parse, you just write Node triggers to do that. Would I have to dig through Haskell code (or hire Haskell developers) to do the same here, or does postgrest support an easier way to do that?

View on HN

You can trigger external actions by connecting PostgreSQL pubsub (LISTEN/NOTIFY) with an external job queue. https://postgrest.com/en/v0.4/intro.html#external-notificati...

A NOTIFY SQL command can be sent out from either a stored procedure or a table trigger. (The docs could use some examples of this, but that's the idea.)

Be aware that Postgres' NOTIFY is not stored/queued in any way. If your external client is not listening, it will get lost.

I would instead have the trigger insert a row into a "pending tasks" table - and then send a NOTIFY.

http://debezium.io/ is a better way to do this.

It uses the logical decoding feature to get all row changes and writes them to a Kafka queue.

This means it can pick up where it left when it crashes.

along the same lines https://github.com/confluentinc/bottledwater-pg

This is meant to be only a data layer; it's not a full backend. Presumably your application events are handled at a different layer in your stack.

That said, you could add event handling inside of Postgresql via triggers and one of the supported procedural languages (like PL/Python)

Postgres supports async notifications, so you could just write a little service which gets a message when a record changes, and put the Stripe logic there. https://postgrest.com/en/v0.4/intro.html#external-notificati...

Not as simple as Parse, I guess, but that's a tradeoff of using lower-level technology.

Reply on news.ycombinator.com