node.js Global connection already exists. Call sql.close() first

Question

I\'m trying to create web services using node.js from an sql server database,in the frontend when i call those 2 webservices simultaneously it throws an error Global connect

Answer 1

Don't read their documentation, I don't think it was written by someone that actually uses the library :) Also don't pay any attention to the names of things, a 'ConnectionPool' doesn't seem to actually be a connection pool of any sort. If you try and create more than one connection from a pool, you will get an error. This is the code that I eventually got working:

const sql = require('mssql');

let pool = new sql.ConnectionPool(config); // some object that lets you connect ONCE
let cnn = await pool.connect(); // create single allowed connection on this 'pool'
let result = await cnn.request().query(query);
console.log('result:', result);
cnn.close(); // close your connection
return result;

This code can be run multiple times in parallel and seems to create multiple connections and correctly close them.

Answer 2

if this problem still bother you, then change the core api. go to node_modules\mssql\lib\base.js at line 1723, add below code before if condition globalConnection = null

Answer 3

From the documentation, close method should be used on the connection, and not on the required module,

So should be used like

var connection = new sql.Connection({
user: '...',
password: '...',
server: 'localhost',
database: '...'
});
connection.close().

Also couple of suggestions,
1. putting res.send in a loop isn't a good idea, You could reply back the entire recordsets or do operations over it, store the resultant in a variable and send that back.
2. Try using promises, instead of callbacks, it would make the flow neater

Answer 4

You have to create a poolConnection try this:

new sql.ConnectionPool(config).connect().then(pool => {

  return pool.request().query("SELECT * FROM MyTable")

  }).then(result => {

    let rows = result.recordset
    res.setHeader('Access-Control-Allow-Origin', '*')
    res.status(200).json(rows);
    sql.close();

  }).catch(err => {

    res.status(500).send({ message: `${err}`})
    sql.close();

  });

Answer 5

In case someone comes here trying to find out how to use SQL Server pool connection with parameters:

var executeQuery = function(res,query,parameters){

   new sql.ConnectionPool(sqlConfig).connect().then(pool =>{

    // create request object
    var request = new sql.Request(pool);

   // Add parameters
    parameters.forEach(function(p) {
    request.input(p.name, p.sqltype, p.value);
    });

    // query to the database
    request.query(query,function(err,result){

            res.send(result);
            sql.close();

    });
 })       
} 

Answer 6

You must use ConnectionPool.

Next function returns a recordset with my query results.

async function execute2(query) {

    return new Promise((resolve, reject) => {

        new sql.ConnectionPool(dbConfig).connect().then(pool => {
            return pool.request().query(query)
        }).then(result => {

            resolve(result.recordset);

            sql.close();
        }).catch(err => {

            reject(err)
            sql.close();
        });
    });


}

Works fine in my code!