postgis trigger automatic calc area

.sql

-- CREATE NEW SCHEMA
CREATE SCHEMA fields;

-- ADD POSTGIS TABLE 
CREATE TABLE fields.parcelas ( 
id serial primary key, 
geom geometry(polygon, 4326),
--geom geometry(polygon, 32616),
centre_northing decimal, 
centre_easting decimal,
centre_latitude decimal, 
centre_longitude decimal,  
latlong_dms varchar, 
area_ha decimal,   
date_created timestamp with time zone DEFAULT now(), 
created_by character varying DEFAULT "current_user"(), 
date_modified timestamp with time zone, 
modified_by character varying
);


-- ADD FUNCTION TRIGGER
CREATE OR REPLACE FUNCTION fields.trigger_function() RETURNS trigger AS $$
BEGIN

 IF (TG_OP = 'INSERT') THEN
	NEW.centre_northing = st_y(st_centroid(NEW.geom)); 
	NEW.centre_easting =st_x(st_centroid(NEW.geom));
	NEW.centre_latitude = st_y(st_centroid(st_transform(NEW.geom,4326))); 
	NEW.centre_longitude = st_x(st_centroid(st_transform(NEW.geom,4326)));
	NEW.latlong_dms = ST_AsLatLonText(st_centroid(st_transform(NEW.geom,4326)));
	NEW.area_ha = ROUND ((st_area(NEW.geom::geography)/10000)::numeric,2) ;
	--NEW.area_ha = ROUND ((st_area(NEW.geom)/10000)::numeric,2) ;

	NEW.date_modified = now();
	NEW.modified_by = "current_user"();
	RETURN NEW;

 ELSIF (TG_OP = 'UPDATE') THEN
	
	IF NOT (NEW.geom ~= OLD.geom) THEN
		NEW.centre_northing = st_y(st_centroid(NEW.geom)); 
		NEW.centre_easting =st_x(st_centroid(NEW.geom));
		NEW.centre_latitude = st_y(st_centroid(st_transform(NEW.geom,4326))); 
		NEW.centre_longitude = st_x(st_centroid(st_transform(NEW.geom,4326)));
		NEW.latlong_dms = ST_AsLatLonText(st_centroid(st_transform(NEW.geom,4326)));
		NEW.area_ha = ROUND ((st_area(NEW.geom::geography)/10000)::numeric,2) ;
		--NEW.area_ha = ROUND ((st_area(NEW.geom)/10000)::numeric,2) ;

		NEW.date_modified = now();
	END IF;
	RETURN NEW;
 END IF;

END;
$$ language plpgsql;


-- ADD TRIGGER 
CREATE TRIGGER trigger_funcions
 BEFORE INSERT OR UPDATE
 ON fields.parcelas
 FOR EACH ROW
 EXECUTE PROCEDURE fields.trigger_function();