PostgresException return null from GCP when call function have an error by constraint FK - npgsql

Question

I am using Google Cloud Platform to host my database postgres 9.6.
I have sent data to force error in FK for an update, in filas = cmd.ExecuteNonQuery() the result is 0 rows, as I hoped. But catch (PostgresException msg_exception) does not recognize the exception and PostgresNotice msg_notice = new PostgresNotice() returns NULL too when try to use the msg_notice.
using(var conn = new NpgsqlConnection(connString)) {
conn.Open();
conn.TypeMapper.MapComposite < DTO_Usuario > ("t_usuario");
using(var transaction = conn.BeginTransaction(IsolationLevel.ReadCommitted)) {
try {
using(NpgsqlCommand cmd = new NpgsqlCommand(# "SELECT ent_usuario_update(#p)", conn)) {
cmd.Parameters.Add(new NpgsqlParameter {
ParameterName = "p",
Value = row_usuario
});
PostgresNotice msg_notice = new PostgresNotice();
try {
filas = cmd.ExecuteNonQuery();
transaction.Commit();
if (filas > 0) {
row_usuario.Nom_usuario = msg_notice.MessageText;
} else {
row_usuario.Nom_usuario = msg_notice.MessageText;
}
} catch (PostgresException msg_exception) {
transaction.Rollback();
row_usuario.Des_cargo = msg_exception.SqlState;
}
return Ok(row_usuario);
}
} catch (NpgsqlException) {
transaction.Rollback();
return NoContent();
}
}
}
My function in Postgres:
CREATE OR REPLACE FUNCTION public.ent_usuario_update(
p_usuario t_usuario)
RETURNS void
update usuario
set des_cargo=p_usuario.des_cargo,
nom_usuario = p_usuario.nom_usuario,
id_organizacion = p_usuario.id_organizacion
where id_instancia = p_usuario.id_instancia
and id_mandante = p_usuario.id_mandante
and id_usuario=p_usuario.id_usuario;
GET DIAGNOSTICS filas = ROW_COUNT;
IF filas == 0 THEN
RAISE INFO 'No se actualizo usuario % en instancia %', p_usuario.id_usuario, p_usuario.id_instancia
using message = 'No actualizo';
ELSE
RAISE INFO 'Actualización Realizada'
using message = 'No actualizo';
END IF;
RETURN;
END;

Answer 1

PostgreSQL notices aren't raised as exceptions, because they're not errors - so try/catch won't yield anything. It's also not possible to simply instantiate a PostgresNotice and expect it to get automatically filled in when you execute a command.
To receive a PostgreSQL notice, simply subscribe to the Notice event on your connection:
conn.Notice += (sender, args) => Console.WriteLine(args.Notice.MessageText);