Re: Using Transaction with if-else in prepared statement

On Wed, May 25, 2022 at 4:13 AM Hui Jackson <jackhts4(at)gmail(dot)com> 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.
>
> const coin = 10
> const senderId = 1
> const receiverId = 2
> await pgPool.query(`
> DO $$
> BEGIN
> if (SELECT coin from app_user where id = $1) >= $3 THEN
> UPDATE app_user set coin = coin - $3 where id = $1;
> UPDATE app_user set coin = coin + $3 where id = $2;
> INSERT INTO coin_history(sender_id, receiver_id, amount)
> VALUES ($1, $2, $3)
>
> END IF;
> END;
> $$`,[senderId, receiverId, coin]);
>
> Error (node:10044) UnhandledPromiseRejectionWarning: error: bind message
> supplies 3 parameters, but prepared statement "" requires 0
>

For debugging, you might try to sending each select, update, and insert in
separate NodeJS query statements. You can do the IF work in NodeJS via a
select for data from Pg.

But at the core of your problem I believe is that you are not configuring
the postgres statement to receive parameters, but your injecting parameters
from Node. From the Pg docs on prepared statements:
https://www.postgresql.org/docs/current/sql-prepare.html

PREPARE fooplan (int, text, bool, numeric) AS
INSERT INTO foo VALUES($1, $2, $3, $4);
EXECUTE fooplan(1, 'Hunter Valley', 't', 200.00);