Custom validation with database

It works:

module.exports.postSignup = [
check('email', 'E-mail already in use').custom((value, { req }) => value !== '[e-mail]'),
...

It doesn’t:

module.exports.postSignup = [
check('email', 'E-mail already in use').custom((value, { req }) => {
  value !== '[e-mail]'
}),
...

The reason why I want to use the example that doesn’t work is because I want to use MySQL query to validate if e-mail address is already in use. Something like this:

module.exports.postSignup = [
check('email', 'E-mail already in use').custom((value, { req }) => {
  const db = require('../db');
  db.query('SELECT email FROM `users` WHERE email = ?'
      , [req.body.email], function(error, results, fields) {
        if (error) throw error;
        if (results.length > 0) {
          return value !== results[0].email;
        };
      });
}),
...

How should I do that? Any ideas?

Thanks!

[gustavohenke]

Eae @barrosfilipe 😉,

The example you gave as not working is because you’re using an arrow function without a return. value => value is the same as value => { return value }, but value => { value } is simply a function that evaluates value, without returning anything.

In the full example for DB validation, you are trying to return from within an async callback. In this case, you should use promises instead. For a detailed explanation, see this popular StackOverflow question.

[gustavohenke]

You should use promises for this. They must be rejected for the validation to be considered as failed.