PostgreSQL trigger function to send notifications when table changes.

notify_event.sql

-- Adapted from http://coussej.github.io/2015/09/15/Listening-to-generic-JSON-notifications-from-PostgreSQL-in-Go/
CREATE OR REPLACE FUNCTION notify_event() RETURNS TRIGGER AS $$
    DECLARE
        data JSON;
        notification JSON;

    BEGIN
        -- Skip notification if row doesn't actually change in UPDATE.
        -- We can accomplish the same thing with a WHERE clause in the CREATE TRIGGER statement,
        -- but only if the trigger watches exclusively for UPDATE events.
        IF TG_OP = 'UPDATE' AND OLD.* IS NOT DISTINCT FROM NEW.* THEN
            RETURN NULL;
        END IF;

        IF TG_OP = 'DELETE' THEN
            data = row_to_json(OLD);
        ELSE
            data = row_to_json(NEW);
        END IF;

        notification = json_build_object(
            'table', TG_TABLE_NAME,
            'action', TG_OP,
            'row', data
        );

        PERFORM pg_notify('events', notification::text);

        -- Result is ignored since we call this function in an AFTER trigger.
        RETURN NULL;
    END;
$$ LANGUAGE plpgsql;


-- Using:
CREATE TRIGGER my_trigger
    AFTER DELETE OR INSERT OR UPDATE ON my_table
    FOR EACH ROW
    EXECUTE PROCEDURE notify_event();