send list of database rows like object to view in nodejs

Question

I'm new in nodejs and expressjs I want to do some query on my database table and show the result in view but i cant do it:

var express = require('express');
var router = express.Router();
var mysql = require('mysql');
var con = mysql.createConnection({
 host: "localhost",
 user: "root",
 password: "",
 database: "imanweb"
});

/* GET home page. */ 
router.get('/', function(req, res, next) {
let objects=['a','b']
con.connect(function(err){
 if(err) throw err;
 con.query("select * from tags", function (err, result) {
 if (err) throw err;
 result.forEach(function(element) {
 objects.push(element);
 console.log("Result: " + element.title);
  }, this);

  });
 })
 console.log("Array: " + objects);
 res.render('index', { title: 'Express' ,objs:objects});
});

module.exports = router;

actually the log of this code is like this:

   Arr:a,b
    Get 200 /410.25 ms --196
    Result:php
    Result:.net

so it seems the last line of my code is running sooner as the past lines(query)!

it's some thing like asynchronous code running!. so when i give objects to objs parameter. there is no query result inside that.

as solution I tried to use then() but i got > undefined then error in my code..

How can I handle that ??

David Stenstrøm · Accepted Answer · 2017-11-07 09:59:52Z

1

You need to put your res.render function inside the callback. Like this:

con.connect(function(err){
  if(err) throw err;
  result.forEach(function(element) {
    objects.push(element);
  }
  res.render('index', { title: 'Express' ,objs:objects});
}, this);

If you send the response outside the callback, your response will be send immediately - it will not wait for the async function.

answered Nov 7, 2017 at 9:59

David Stenstrøm

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1 Comment

David Stenstrøm Over a year ago

Then you'll have to nest the callbacks. Or - as I would recommend - use a promise library. Then you can do then and catch - and avoid nested callbacks within nested callbacks.

Pedro Henrique · Accepted Answer · 2017-11-08 22:43:26Z

0

This works? If not try use async module to do this forEach method in your code. I've this issue one time and the problem was on forEach.

edited Nov 8, 2017 at 22:43

answered Nov 8, 2017 at 22:27

Pedro Henrique

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