How to send multiple responses in node js - mysql

Question

How to send multiple response in node js? In this code I want to send data and data1
function(req, res){
var classValue = req.query.classID;
var sql = "SELECT * FROM class WHERE `class_name` ='"+classValue+"'";
connection.query(sql, function(err, data){
if(data.length){
var sql1 = "SELECT * FROM book WHERE `class_id` ='"+data[0].class_id+"'";
connection.query(sql1, function(err, data1){
res.status(200).send(data1);
res.status(200).send(data);
});
}
});
}

Answer 1

Calling send will end the connection, so you can only call it once. You can send back a complex structure as JSON easily like this:
res.json( { data, data1 } );
Note that you have a path where data.length might be zero that still needs to be handled. You might consider something like this:
function(req, res, next){
var classValue = req.query.classID;
var sql = "SELECT * FROM class WHERE `class_name` ='" + classValue + "'";
connection.query(sql, function(err, data) {
if (err) return next(err); // <-- handle errors
if (data.length) {
var sql1 = "SELECT * FROM book WHERE `class_id` ='" + data[0].class_id + "'";
connection.query(sql1, function(err, data1) {
if (err) return next(err); // <-- handle errors
res.json( { data, data1 } );
});
}
else {
res.json( {data: null, data1: null} ); // or treat it as an error?
}
});
}
If it's an error condition that the first query gives no results, then you can treat it as an error. Note that I also added error handling using the next function (assuming you're using Express routing).