PostGIS Trigger doesn't work

Question

The trigger below don't works and I need that when a new pipeline (adutoras) is inserted or updated, the procedure check what are the municipalities (municipios) that intersects the pipes and put the names of the municipalities inside the field "municipios_abastecidos".

CREATE OR REPLACE FUNCTION topology_fields() 
RETURNS "trigger" AS
$$
BEGIN
NEW.municipios_abastecidos:=(
                      SELECT string_agg(municipios.nome,', ')
                      FROM municipios, adutoras
                      WHERE ST_Intersects(adutoras.geom, municipios.geom)
                      AND adutoras.gid = NEW.gid
                    );
RETURN NEW;
END; 
$$
LANGUAGE 'plpgsql';


CREATE TRIGGER fill_topology_fields
BEFORE INSERT OR UPDATE ON adutoras
FOR EACH ROW EXECUTE PROCEDURE topology_fields();

Thanks in Advance

Answer 1

Solved,

CREATE OR REPLACE FUNCTION topology_fields()
RETURNS trigger AS
$$
BEGIN

SELECT string_agg(municipios.nome,', ')
INTO NEW.municipios_abastecidos
FROM municipios
WHERE ST_Intersects(NEW.geom, municipios.geom);

RETURN NEW;
END;
$$
LANGUAGE 'plpgsql';

CREATE TRIGGER fill_topology_fields
BEFORE INSERT OR UPDATE ON adutoras
FOR EACH ROW EXECUTE PROCEDURE topology_fields();

Appreciate the help from PostGIS-User List, especially Ralf Suhr and Tom Glancy, thank you so much!