Concluded both methods shared:
1. one query per each call for using prepared statement
await pgPool.query('BEGIN;');
const sender = (await pgPool.query('SELECT coin from app_user where id = $1;',[senderId])).rows[0];
if(sender.coin >= amount){
await pgPool.query('UPDATE app_user set coin = coin - $1 where id = $2;',[coin, senderId]);
await pgPool.query('UPDATE app_user set coin = coin + $1 where id = $2;',[coin, receiverId]);
await pgPool.query('INSERT INTO coin_history(sender_id, receiver_id, amount) VALUES ($1, $2, $3)',[senderId, receiverId, coin]);
await pgPool.query('COMMIT;');
}else{
await pgPool.query('END;');
}
2. Use constraint
CREATE TABLE app_user( id integer, coin numeric CHECK (coin >= 0)
);
On Wed, May 25, 2022 at 07:12:49PM +0800, Hui Jackson wrote:
> I am trying to make transaction in nodejs
> The logic will be check if sufficient coin in sender's amount, if
> sufficient then do transaction.
> I am new to postgres, not sure if this is a right way to do so, if you have
> a better solution, please let me know, thank you.
I would do i by issuing *only*
INSERT INTO coin_history(sender_id, receiver_id, amount) VALUES
and then changing coin data with triggers plus adding constraints that
app_user.coin can never be < 0.
depesz
