Re: Strange behavior of transcations

Correct, he is reading from the connection while writing to it.  Unless all
the rows have been read, you can't use it to do a write, at the protocol
level.  Use two connections from the pool for this, one for the read, and
the other for the writes.

On Sun, Jun 5, 2022, 10:29 AM David G. Johnston <david.g.johnston@gmail.com>
wrote:

> On Sunday, June 5, 2022, Hui Jackson <jackhts4@gmail.com> wrote:
>
>> I am working on node-postgres and there is a strange transactions.
>> The function aims at locking user's wallet until the refund process is
>> complete, then will update item's has_refund to true.
>> The problem I am facing is the program return no error, but the database
>> is not updated. Unless I spam the function for multiple times then the
>> value is updated.
>> If I remove begin and commit, then the function work perfectly.
>> const refundService = (itemId) =>{
>>     await pgPool.query('BEGIN;');
>>     const users = (await pgPool.query('SELECT * from app_user where
>> $1=ANY(purchase_list);', [ itemId ])).rows;
>>     for(let i = 0; i < users.length; i++){
>>         refund(users[i])
>>     }
>>     await pgPool.query('UPDATE item_lists SET has_refund = $1 where id =
>> $2;', [true,  itemId ]);
>>     await pgPool.query('COMMIT;');
>> }
>>
>> const refund = (user) =>{
>>     const refund = 10
>>     await pgPool.query('UPDATE app_user SET wallet = wallet + $1', [
>> refund ]);
>> }
>>
>
>
> I think you are mis-using your pool.  If you want transactions you need
> checkout a connection from the pool and use it for every command in the
> transaction.  The one-shot query method on the pool is meant for standalone
> commands.  I say think because I’m unsure why you’d get no updates instead
> of updates but no transaction…
>
> David J.
>
>