how does mysql.createPool work?

[MassMessage]

how does mysql.createPool work? let's say i have the following code:

const getConn = () => {
    const connection = mysql.createPool({
        host: process.env.DB_HOST,
        user: process.env.DB_USER,
        password: process.env.DB_PASS,
        database: process.env.DB_NAME
    });
    return connection;
}

const foo = () => {
    const coon = getConn();
    coon.query('select * from YYY',
        function(err, results, fields) {
            console.log(results);
        }
    );
}


const baa = () => {
    const coon = getConn();
    coon.query('select * from ZZZ',
        function(err, results, fields) {
            // do something
        }
    );
}

i do call foo and later on baa. in the call foo the connection is created and in baa and subsequents call to getConn i'll get just the same connection instance created by foo, is that right?

[sidorares]

you are creating a new pool instance in getConn, which manages its own set of connections. In your example connections are not shared or reused.

What you should do instead ( I'm using async api but callback version is similar )

const pool = mysql.createPool(connectOptions);

const foo = async () => {
  const conn = await pool.getConnection();
  const [rows] = conn.query('select * from YYY');
  conn.release();
  console.log(rows);
};

const baa = async () => {
  // or just do .query() on a pool, it'll do .getConnection + query + release internally
  const [rows] = pool.query('select * from YYY');
  console.log(rows);
};

[MassMessage]

you are creating a new pool instance in getConn, which manages its own set of connections. In your example connections are not shared or reused.

What you should do instead ( I'm using async api but callback version is similar )

const pool = mysql.createPool(connectOptions);

const foo = async () => {
  const conn = await pool.getConnection();
  const [rows] = conn.query('select * from YYY');
  conn.release();
  console.log(rows);
};

const baa = async () => {
  // or just do .query() on a pool, it'll do .getConnection + query + release internally
  const [rows] = pool.query('select * from YYY');
  console.log(rows);
};

I"ve tried to make a version without callbacks but i'm getting error from query(). code:

const getName2 =  (conn: mysql.PoolConnection, code:number): string | null =>
{
    const [results] = conn.query('select bares_nome from bares where bares_cod = ?', [code]);
        
    if(IsRowDataPacket(results) && results.length === 0)
    { 
        return null;
    }

    interface IBar { bares_nome: string; }
    const data = results as IBar[];
    const r:IBar = data[0];
    return r.bares_nome;
}

but on results var i'm getting the error:

Type 'Query' is not an array type.ts(2461)

[sidorares]

is that just a types error ( e.i does it work as expected without a type check )?

[MassMessage]

is that just a types error ( e.i does it work as expected without a type check )?

it doesn't compile. I get the error:

Type error: Type 'Query' is not an array type.