PostgreSQL trigger function for geometry change notification

geomchange_plpgsql

CREATE OR REPLACE FUNCTION redis_pubsub.notifygeometrychange_trigger()
  RETURNS trigger AS
$BODY$
DECLARE
  message text;
  geom geometry;
  xmin double precision;
  ymin double precision;
  xmax double precision;
  ymax double precision;
BEGIN
  
  message := concat_ws(';', TG_TABLE_NAME, TG_OP);
  IF TG_OP = 'UPDATE' THEN
    IF NOT st_equals(OLD.geometria, NEW.geometria) THEN
      IF NEW.geometria IS NULL THEN
        geom := OLD.geometria;
      ELSE
        geom := NEW.geometria;
      END IF;
    END IF;
  ELSIF TG_OP = 'INSERT' THEN
    geom := NEW.geometria;
  ELSIF TG_OP = 'DELETE' THEN
    geom := OLD.geometria;
  END IF;
  
  xmin := st_xmin(box2d(geom));
  ymin := st_ymin(box2d(geom));
  xmax := st_xmax(box2d(geom));
  ymax := st_ymax(box2d(geom));
  message := concat_ws(';', message, xmin::text, ymin::text, xmax::text, ymax::text);
  PERFORM redis_pubsub.notify('mapproxy', message, '127.0.0.1', 6379);
  RETURN NULL;
END;
$BODY$
  LANGUAGE plpgsql VOLATILE;