Not getting a return object from a MySQL query in NodeJS

Question

I'm making a logging system in NodeJS with MySQL DB. First I do the connection like this:

const con = mysql.createConnection({
  host     : 'localhost',
  user     : 'dbuser',
  password : 'dbpass',
  database : 'dbname',
  port     : 3306,
  multipleStatements : true
});

Then when I do a query to get users data I do the following query.

var user;
con.query('SELECT * FROM users WHERE email = ?', email, function(err, rows) {
    if (err) throw err;
    else {
       user = rows[0];
    }
});

But when I finally compare any of the fields of the user returned I get an error:

if (tools.hashPassword(password) == user.hash) {
    // Do stuff
}

The error is TypeError: Cannot read property 'hash' of undefined. Any suggestion?

ponury-kostek · Accepted Answer · 2018-11-29 11:03:10Z

2

con.query("SELECT * FROM users WHERE email = ?", email, function (err, rows) {
    if (err) {
        throw err;
    } else {
        if (!rows.length) {
            throw new Error("User not found");
        }
        const user = rows[0];
        if (tools.hashPassword(password) == user.hash) {
            // Do stuff
        }
    }
});

answered Nov 29, 2018 at 11:03

ponury-kostek

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Comments

Slawomir Wozniak · Accepted Answer · 2018-11-29 18:18:22Z

0

The fact is that you are getting the result, but it is asynchronous. Therefore at the time you check for user's property hash, the object itself has not loaded yet. You should put your comparison in the callback like this:

con.query('SELECT * FROM users WHERE email = ?', email, function(err, rows) {
  if (err) throw err;
  else {
     if (tools.hashPassword(password) === rows[0].hash) {
        // Do stuff
     }
  }
});

// This stuff happens usually BEFORE the query's callback,
// due to Node.js asynchronous nature

answered Nov 29, 2018 at 18:18

Slawomir Wozniak

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