Render multiple queries in Node Express

Question

I am working with Node.js (express) and MySQL and I have had problems trying to make several queries in the same route. The error it throws is:

Can't set headers after they are sent.

And my code is this:

router.post('/test', function (req, res, next){
db.query("select COLUMN_NAME from INFORMATION_SCHEMA.COLUMNS where 
TABLE_NAME = 'registros';", function (error, results, fields) {

if (error) throw error;
res.render('test', {
columnNames: results
});});
db.query("SELECT * FROM registros", function (error, resp, fields) {

if (error) throw error;
res.render('test', {
dataRegistros: resp
});});

});

I understand that it may be because it is rendering twice in the same route. What would be the correct method to make several SQL queries and return them to a file in view?

Regards!

Paul · Accepted Answer · 2018-09-09 14:34:33Z

1

According to mysql nodejs driver you can setup it o combine the queries and return an array with results

You must set this when you create the connection:

mysql.createConnection({multipleStatements: true});

Then make the request with both queries

router.post('/test', function (req, res, next) {

  var queries = [
    "select COLUMN_NAME from INFORMATION_SCHEMA.COLUMNS where TABLE_NAME = 'registros'",
    "SELECT * FROM registros"
  ];

  db.query(queries.join(';'), function (error, results, fields) {

    if (error) throw error;

    res.render('test', {
      columnNames: results[0], // First query from array
      dataRegistros: resp      // Second query from array
    });

  });

});

But let me ask a question, why would you need to query column names when actually you query all rows and can get columns from there?

answered Sep 9, 2018 at 14:34

Paul

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1 Comment

Kryphon Over a year ago

Hi. The reason I did that was ... just to experiment! I asked myself what happens if I need to make several queries from a single route and send them. I wanted to populate an html table by first getting the names of the columns and then the entire record for the body of the table. Thanks, I'll try what you suggested!

esakki · Accepted Answer · 2018-09-10 05:26:30Z

0

To make several queries from a single route use async npm library

npm install --save async

then use parallel method and functions to make the several queries for database with the callback.

async.parallel({
   one: function(callback) {
      callback(null, 'abc\n');
   },
   two: function(callback) {
     callback(null, 'xyz\n');
   }
}, function(err, results) {
    if (error) throw error;
      res.render('test', {
        columnNames: results.one, 
        dataRegistros: results.two      
     });
});

answered Sep 10, 2018 at 5:26

esakki

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