Platformatic DB sql-events module

The Platformatic DB sql-events uses mqemitter to publish events when entities are saved and deleted.

These events are useful to distribute updates to clients, e.g. via WebSocket, Server-Sent Events, or GraphQL Subscritions. When subscribing and using a multi-process system with a broker like Redis, a subscribed topic will receive the data from all the other processes.

They are not the right choice for executing some code whenever an entity is created, modified or deleted, in that case use @platformatic/sql-mapper hooks.

Install

You can use together with @platformatic/sql-mapper.

npm i @platformatic/sql-mapper @platformatic/sql-events

Usage

const { connect } = require('@platformatic/sql-mapper')
const { setupEmitter } = require('@platformatic/sql-events')
const { pino } = require('pino')

const log = pino()

async function onDatabaseLoad (db, sql) {
  await db.query(sql`CREATE TABLE pages (
    id SERIAL PRIMARY KEY,
    title VARCHAR(255) NOT NULL
  );`)
}
const connectionString = 'postgres://postgres:postgres@localhost:5432/postgres'
const mapper = await connect({
  connectionString,
  log,
  onDatabaseLoad,
  ignore: {},
  hooks: {
    Page: {
      find: async function(_find, opts) {
        console.log('hook called');
        return await _find(opts)
      }
    }
  }
})

setupEmitter({ mapper, log })

const pageEntity = mapper.entities.page

const queue = await mapper.subscribe([
  pageEntity.getSubscriptionTopic({ action: 'save' }),
  pageEntity.getSubscriptionTopic({ action: 'delete' })
])

const page = await pageEntity.save({
  input: { title: 'fourth page' }
})

const page2 = await pageEntity.save({
  input: {
    id: page.id,
    title: 'fifth page'
  }
})

await pageEntity.delete({
  where: {
    id: {
      eq: page.id
    }
  },
  fields: ['id', 'title']
})

for await (const ev of queue) {
  console.log(ev)
  if (expected.length === 0) {
    break
  }
}

process.exit(0)

API

The setupEmitter function has the following options:

• mq - an instance of mqemitter, optional.

The setupEmitter functions adds the following properties to the mapper object:

• mq — an instance of mqemitter
• subscribe(topics) — a method to create a node Readable that will contain the events emitted by those topics.

Each entity of app.platformatic.entities will be augmented with two functions:

• entity.getPublishTopic({ ctx, data, action })
• entity.getSubscriptionTopic({ ctx, action })

Where ctx is the GraphQL Context, data is the object that will be emitted and action is either save or delete.