Node Js with mySQL return Null-CodePudding

I am trying to Skip the data if there is nothing return from the mySql Database How can I achieve it?

Here is my code

const mysql = require('mysql2');
function dbconnection() {
    const connection = mysql.createConnection({
    host: '127.0.0.1',
    user: 'root',
    password: 'password',
    database: 'DB'
});
var Data_export = dbconnection();
      Data_export.query(sql, function (err, data, fields) {
        if (err) throw err;
        if (data !== Null) {
            const jsonData = JSON.parse(JSON.stringify(data));
            fastcsv
                .write(jsonData, { headers: true })
                .on("finish", function () {
                    console.log("Write to file.csv successfully!");
                })
                .pipe(ws);
        } else { console.log("Nothing"); }

But it doesn't work Any help would be greatly appreciated, thanks!

CodePudding user response：

You must return something on your connection's function, and the code has some syntax issues.

It must work:

function dbconnection() {
    const connection = mysql.createConnection({
        host: '127.0.0.1',
        user: 'root',
        password: 'password',
        database: 'DB'
    });

    return connection;
}

var Data_export = dbconnection();
Data_export.query(sql, function (err, data, fields) {
    if (err) throw err;
    if (data !== Null) {
        const jsonData = JSON.parse(JSON.stringify(data));
        fastcsv
            .write(jsonData, { headers: true })
            .on("finish", function () {
                console.log("Write to file.csv successfully!");
            })
            .pipe(ws);
    } else { 
        console.log("Nothing"); 
    }
});

CodePudding user response：

I found the solution

Because it is a return array from the mysql, So instead of

        if (data !== Null) {
            const jsonData = JSON.parse(JSON.stringify(data));
            fastcsv
                .write(jsonData, { headers: true })
                .on("finish", function () {
                    console.log("Write to file.csv successfully!");
                })
                .pipe(ws);}

I use this one

        if (data.length !==0) {
            const jsonData = JSON.parse(JSON.stringify(data));

            //write duplication to CSV file 
            fastcsv
                .write(jsonData, { headers: true })
                .on("finish", function () {
                    console.log("Write to file.csv successfully!");
                })
                .pipe(was); }