node-red-contrib-postgres-listen

A Node-RED node to listen to pg_notify

Install

Run the following command in the root directory of your Node-RED install

npm install node-red-contrib-postgres-listen

Overview

This add-on, allows to listen to PostgreSQL pg_notify mechanism.

The node takes two parameters :

• postgresdb : The PostgreSQL connection configuration
• channel : The channel name specified in the pg_notify command

PostgreSQL sample code

1. Create a base table:

    CREATE TABLE realtime
    (
        id INTEGER DEFAULT nextval('realtime_id_seq'::regclass) NOT NULL,
        title CHARACTER VARYING(128),
        PRIMARY KEY (id)
    );
   

2. Create a trigger on the table:

    CREATE TRIGGER "updated_realtime_trigger"
      BEFORE INSERT OR DELETE OR UPDATE ON realtime
      FOR EACH ROW
    EXECUTE PROCEDURE notify_realtime()
   

3. Create a trigger function:

    CREATE FUNCTION public.notify_realtime()
        RETURNS trigger
        LANGUAGE 'plpgsql'
        COST 100.0
        VOLATILE NOT LEAKPROOF 
    AS $BODY$
   
    BEGIN
        PERFORM pg_notify('addedrecord', '' || row_to_json(NEW));
        RETURN NEW;
    END;
    $BODY$;
   

Result

The node will produce a message like that :

{"name":"notification","length":47,"processId":16147,"channel":"addedrecord","payload":{"id":2,"title":"plopcsd"}}

All fields are generated by Postgres with payload being the content of the table row.

Changelog

• 0.2.0 : Removed the postgres configuration Node and created a dependency to https://flows.nodered.org/node/node-red-contrib-postgres making it possible to have both nodes installed.