How can I throw a custom error with express-validator?

Question

I am validating a form through the POST method. I want to push an error into express-validator when an email address is already registered, so when I do req.validationErrors() it is included. Something like this:

req.checkBody('inputFirstName', 'First name empty').notEmpty();
req.checkBody('inputLastName', 'Last name empty').notEmpty();
db.User.find({email: req.body.inputEmail}, function (err, user){
        if(user){
            var error = {param: "inputEmail", msg: "Email address already registered", value: ''};
            expressValidator._errors.push(error);
        }
    });

Thanks.

Answer 1

You can do something like this:

req.checkBody('inputFirstName', 'First name empty').notEmpty();
req.checkBody('inputLastName', 'Last name empty').notEmpty();
var errors = req.validationErrors();
db.User.find({email: req.body.inputEmail}, function (err, user){
        if(user){
            var error = {param: "inputEmail", msg: "Email address already registered", value: req.body.email};
            if (!errors) {
                errors = [];
            }
            errors.push(error);
        }

        // Here need  to be next part of action - not outside find callback!
    });

But I think it's a bad idea to put some mongoose validation on request side validation. You can use some schema methods, e.g. pre save, make validation there.

Answer 2

Here is one example that you should put in your validator:

   // Validates data when registering new user.
   exports.registerNewUser = [        
     body('email').
       exists().withMessage("Email is required").
       isEmail().withMessage("Not a valid email").bail().
       // bail() is important so that in case some of previous validations fail, you don't call db function
       custom(async (val) => {
        // Check if the email is already taken
        try {
            const user = await User.getOneUserByEmail({email: val});
            // check for example if user exists or that it is not closed
            if(user && user.status!=="closed") return false;
            else return true;
        } catch(error) {
            // if there is an error, always return false
            console.log(error);
            return false;
        }
    }).withMessage("Email already taken")
  ]

You should also import:

const { body } = require('express-validator/check');