A Publish/Subscribe implementation on top of PostgreSQL NOTIFY/LISTEN
npm install pg-pubsubA Publish/Subscribe implementation on top of PostgreSQL NOTIFY/LISTEN
``bash`
npm install pg-pubsub --save
* Postgres >= 9.4
`js`
const PGPubsub = require('pg-pubsub');
const pubsubInstance = new PGPubsub(uri[, options]);
`js`
{
[log]: Function // default: silent when NODE_ENV=production, otherwise defaults to console.log(...)
}
* addChannel(channelName[, eventListener]) – starts listening on a channel and optionally adds an event listener for that event. As PGPubsub inherits from EventEmitter one can also add it oneself. Returns a Promise that resolves when the listening has started.NOTIFY channelName, '{"hello":"world"}'
* removeChannel(channelName[, eventListener]) – either removes all event listeners and stops listeneing on the channel or removes the specified event listener and stops listening on the channel if that was the last listener attached.
* publish(channelName, data) – publishes the specified data JSON-encoded to the specified channel. It may be better to do this by sending the query yourself using your ordinary Postgres pool, rather than relying on the single connection of this module. Returns a Promise that will become rejected or resolved depending on the success of the Postgres call.EventEmitter
* close(): Promise
* All EventEmitter methods are inherited from
#### Simple
`javascript
const pubsubInstance = new PGPubsub('postgres://username@localhost/database');
await pubsubInstance.addChannel('channelName', function (channelPayload) {
// Process the payload – if it was JSON that JSON has been parsed into an object for you
});
await pubsubInstance.publish('channelName', { hello: "world" });
`
The above sends NOTIFY channelName, '{"hello":"world"}' to PostgreSQL, which will trigger the above listener with the parsed JSON in channelPayload.
#### Advanced
`javascript
const pubsubInstance = new PGPubsub('postgres://username@localhost/database');
await pubsubInstance.addChannel('channelName');
// pubsubInstance is a full EventEmitter object that sends events on channel names
pubsubInstance.once('channelName', channelPayload => {
// Process the payload
});
`
Creating a PGPubsub instance will not do much up front. It will prepare itself to start a Postgres connection once the first channel is added and then it will keep a connection open until its shut down, reconnecting it if it gets lost, so that it can constantly listen for new notifications.
- setup a postgres database to run the integration tests
- the easist way to do this is via docker, docker run -it -p 5432:5432 -e POSTGRES_DB=pgpubsub_test postgres
-
For an all-in-one command, try:
`sh``fire up a new DB container, run tests against it, and clean it up!
docker rm -f pgpubsub_test || true && \
docker run -itd -p 5432:5432 -e POSTGRES_DB=pgpubsub_test --name pgpubsub_test postgres && \
npm test && \
docker rm -f pgpubsub_test