Fast and easy CSV download by streaming for node-express

download-csv

    var csv = require('fast-csv');
    var mysql = require('mysql');
    var connection = mysql.createConnection(config.mysql);

    var pool = mysql.createPool({
        connectionLimit: 10,
        host: config.mysql.host,
        user: config.mysql.user,
        password: config.mysql.password,
        database: config.mysql.database,
        port: config.mysql.port
    });

    
    pool.getConnection(function(err, connection) {
        if (err) {
            console.log('connection error', err);
        } else {
        
            var csvStream = csv
                .createWriteStream({
                    headers: true
                });
        
            res.setHeader('Content-disposition', 'attachment; filename=download.csv');
            res.setHeader('Content-type', 'text/csv');
            csvStream.pipe(res);
        
            var sql = connection.query({
                sql: query, 
                values: []
            }).on('result', function(row) {
                csvStream.write(row);
            }).on('end', function() {
                csvStream.end();
                connection.release();
            });
        }
    });

You can also use the stream transform

var stream = require('stream');

connection.query('select * from bigdata')
  .stream()
  .pipe(stream.Transform({
    objectMode: true,
    transform: function(row,encoding,callback) {
      // do something with data...
      callback()
    }
   })
   .on('finish',() => connection.end() )