pg-pubsub

PG PubSub

A Publish/Subscribe implementation on top of PostgreSQL NOTIFY/LISTEN

Installation

npm install pg-pubsub --save

Requirements

The pg npm package has to be installed. Also – at least node 0.12 or iojs has to be used.

Usage

Simple:

var pubsubInstance = new PGPubsub('postgres://username@localhost/database');
 
pubsubInstance.addChannel('channelName', function (channelPayload) {
  // Process the payload – if it was JSON that JSON has been parsed into an object for you 
});
 
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.

More advanced variant:

var pubsubInstance = new PGPubsub('postgres://username@localhost/database');
 
pubsubInstance.addChannel('channelName');
 
// pubsubInstance is a full EventEmitter object that sends events on channel names 
pubsubInstance.once('channelName', function (channelPayload) {
  // Process the payload 
});

Methods

addChannel(channelName[, eventListener]) – starts listening on a channel and optionally adds an event listener for that event. As PGPubsub inherits from EventEmitter one also add it oneself.
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 NOTIFY channelName, '{"hello":"world"}' 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.
close – closes down the database connection and removes all listeners. Useful for graceful shutdowns.
All EventEmitter methods are inherited from EventEmitter

Description

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.