Connect to a postgres-database and wait for a NOTIFY of the database. This notify-event triggers a function, which receives the payload as EDN if the payload was initially encoded as JSON (for example with postgres' function row_to_json().

A trigger for a table 'events' can be configured like this:

-- language: PLpgSQL
-- Define function for notify-event
CREATE OR REPLACE FUNCTION PUBLIC.NOTIFY() RETURNS trigger AS
$BODY$
BEGIN
PERFORM pg_notify('new_event', row_to_json(NEW)::text);
RETURN new;
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE COST 100;)

-- Creates trigger and binds it to \"events\"-table
CREATE TRIGGER new_event
AFTER INSERT
ON events
FOR EACH ROW
EXECUTE PROCEDURE PUBLIC.NOTIFY();

Require latest version of postgres-listener in your project.clj (check latest version in the badge as this string is very likely to be forgotten on new releases):

:dependencies [[de.hhu.cn/postgres-listener "0.1.2"]]

You can then use it in your code to connect to the database, which provides the NOTIFY channel and add a listener to the corresponding LISTEN event. If your table is configured as shown above, you can react to the trigger new_event like this:

(require '[postgres-listener.core :as pgl])

(pgl/connect {:host "localhost" :port 5432 :database "postgres" :user "postgres" :password "postgres"})
(pgl/arm-listener (fn [payload] (println payload)) "new_event")

Copyright © 2017 Christian Meter

Distributed under the MIT license.