Listen & Notify

Overview

PostgreSQL provides simple publish and subscribe (Pub/Sub) messaging support using the NOTIFY, LISTEN and UNLISTEN commands. It has the concept of a channel that a client can both publish to and subscribe to. The server sends any notifications published to a channel to clients listening on that channel. PostgreSQL channels are not persisted, for instance if a notification is sent to a channel that has no one listening, that notification is lost.

Listening

Use listen(on:consume:) to listen for notifications on a given channel and receive every notification published to that channel via an AsyncSequence. When you exit the closure provided, PostgresNIO sends the relevant UNLISTEN command.

try await connection.listen(on: "channel") { notifications in
    for try await notification in notifications {
        // a notification item includes the payload string communicated along with the notification
        print(notification.payload)
    }
}

Notifying

You can send notifications to a channel using the NOTIFY command.

try await connection.query(#"NOTIFY "channel", 'bar';"#)