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 connection already exists. Call sql.close() first .

Any Solution ?

var express = require('express');
var router = express.Router();
var sql = require("mssql");

router.get('/Plant/:server/:user/:password/:database', function(req, res, next) {

    user = req.params.user;
    password = req.params.password;
    server = req.params.server;
    database = req.params.database;


    // config for your database
    var config = {
        user: user,
        password: password,
        server: server,
        database:database

    };

    sql.connect(config, function (err) {



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

        // query to the database and get the records
        request.query("SELECT  distinct PlantName FROM MachineryStateTable"
            , function (err, recordset) {

                if (err) console.log(err)
                else {

                    for(i=0;i<recordset.recordsets.length;i++) {
                        res.send(recordset.recordsets[i])
                    }

                }
               sql.close();

            });

    });

});





router.get('/Dep/:server/:user/:password/:database/:plantname', function(req, res, next) {

    user = req.params.user;
    password = req.params.password;
    server = req.params.server;
    database = req.params.database;
    plantname = req.params.plantname;

    // config for your database
    var config = {
        user: user,
        password: password,
        server: server,
        database:database

    };

    sql.connect(config, function (err) {



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

        // query to the database and get the records
        request.query("SELECT  distinct DepName FROM MachineryStateTable where PlantName= '"+plantname+"'"
            , function (err, recordset) {

                if (err) console.log(err)
                else {

                    for(i=0;i<recordset.recordsets.length;i++) {
                        res.send(recordset.recordsets[i])

                    }
                    sql.close();
                }

            });
    });
});



module.exports = router;

Answer 1

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 2

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 3

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!