How to handle Multiple Connections dynamically?

Hey, I was looking at the link that describes how to handle multiple connections. In the example, there are 2 hard coded connections. I’m building an app that has many users and I’m trying to figure out how to allow them to not get errors if they query the database at the exact same time or before another query is finished.

The following is what I’m using in a nodejs app running on a Linux machine. It works as long as nobody makes a request before another request is finished. Otherwise with the following code I still get Error: Global connection already exists. Call sql.close() first.

const settings  = require('./settings');
const sql = require('mssql');

exports.execSql = async function(sqlquery) {
  try {
    let pool = await new sql.connect(settings.config);
    let result = await pool.request().query(sqlquery);
    return {success: result};
  } catch (err) { 
    return {err: err};
  } finally {
    sql.close(); //closing connection after request is finished.
  }
};

sql.on('error', err => {
  // ... error handler 
  console.log('sql errors', err);
});

The hardcoded example from the docs assumes there are only 2 connections. How do I modify the above to handle a dynamic number of connections?

[patriksimek]

Try this:

const settings  = require('./settings');
const sql = require('mssql');

exports.execSql = async function(sqlquery) {
  const pool = new sql.ConnectionPool(settings.config);
  pool.on('error', err => {
    // ... error handler 
    console.log('sql errors', err);
  });

  try {
    await pool.connect();
    let result = await pool.request().query(sqlquery);
    return {success: result};
  } catch (err) { 
    return {err: err};
  } finally {
    pool.close(); //closing connection after request is finished.
  }
};

[patriksimek]

@betweenbrain Calling pool.close() in execSql is not a good idea - once you close a pool, you can no longer acquire a connection from that pool. That means that all subsequent requests will fail.

The good idea is to export a close method and close the pool when you’re absolutely sure there will be no more requests to make (e.g. when application closes).