A Publish/Subscribe implementation on top of PostgreSQL NOTIFY/LISTEN
npm install pg-pubsub --save
The pg
npm package has to be installed. Also – at least node 0.12 or iojs has to be used.
Simple:
var pubsubInstance = new PGPubsub('postgres://username@localhost/tablename');
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/tablename');
pubsubInstance.addChannel('channelName');
// pubsubInstance is a full EventEmitter object that sends events on channel names
pubsubInstance.once('channelName', function (channelPayload) {
// Process the payload
});
- addChannel(channelName[, eventListener]) – starts listening on a channel and optionally adds an event listener for that event. As
PGPubsub
inherits fromEventEmitter
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. - close – closes down the database connection and removes all listeners. Useful for graceful shutdowns.
- All EventEmitter methods are inherited from
EventEmitter
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.
npm test
or to watch, install grunt-cli
then do grunt watch