How to check is user already exist with customValidators in express-validator?

问题

I have a problem to return boolean (true or false) if user already exist or not in custom express-validator. So far I manage to work it in this way:

app.use(expressValidator({
    customValidators: {
        isUsernameAvailable: function (username) {
            return User
                    .findOne({ 'username': username })
                    .then(function (user) {
                        if (user) {
                            throw new Error('User already exist')
                        }
                    }
        }
    }

The idea is to return boolean (corresponding the name: isUsernameAvailable) not Promise or Object, but I don't know how.

I used it to check it in this way:

module.exports = {
    create: (req, res) => {
        let user = req.body

        ...
        req.check('username', 'This username is already taken.').isUsernameAvailable()
        ...
    }
}

回答1:

i taken more time to get easy and simplify code for do it

this is my code i used it

router.post('/signup', [
        check('username').notEmpty().withMessage('must be not null').
            .custom((value, {req, loc, path}) => {
                return Users.findOne({
                    where: {
                        username: req.body.username,
                    }
                }).then(user => {
                    if (user) {
                        return Promise.reject('Username already in use');
                    }
                });
            })
    ], (req, res) => {
        const errors = validationResult(req);
        if (!errors.isEmpty()) {
            return res.status(422).json({errors: errors.array()});
        } else {
            // Do everything or create new user
        }

    });

回答2:

you haven't described how your "check" function will know if the username is a duplicate or not, but I will say that I can't think of a scalable solution that doesn't require a trip to some form of data store (database being the most common). In Node, that means an asynchronous call involving a callback or Promise unless you really want to work hard to make it synchronous.

And honestly, any multiuser app with uniqueness requirements is going to get into trouble eventually with a check like you describe because your check and create steps will not be inside a single atomic transaction.

Far better and more scalable to simply apply a unique index to the field in the database, then handle that error appropriately in your app code.

来源：https://stackoverflow.com/questions/40376557/how-to-check-is-user-already-exist-with-customvalidators-in-express-validator