Mongoose object id is null

I am creating a Registration (Mongoose Schema) object and I need to set it Id

in User

with this line:registrationId: registration._id});

However, Id

still null

even if it's a callback function? When I check the database, the Register has an Id, of course, but not in the callback. How to set Id

in Registration

in User

?

Edit2: changed to minimal example. It gives out two times null

.

exports.create = function(req, res) {
  Registration.create(req.body, function(err, registration) {
    if(err) { return handleError(res, err); }

    console.log(registration._id);
    console.log(registration.id);

    return res.json(201, registration);
  });
};

      

        
        
        
      

    

Edit: This is the outline (I haven't used some of the fields that are not required):

'use strict';

var mongoose = require('mongoose'),
    Schema = mongoose.Schema;

var RegistrationSchema = new Schema({

    isReservation: Boolean,

    //Id of the trip
    tripId: String,

    //socialMutuality
    codeGerechtige: String,
    socialMutualityNumberParent1: String,
    socialMutualityNumberParent2: String,

    //contact
    userId: String,
    firstnameContact: String,
    lastnameContact: String,
    emailContact: String,
    streetContact: String,
    streetNumberContact: String,
    zipcodeContact: String,
    busContact: String,
    cityContact: String,
    phoneContact: String,
    gsmContact: String,
    socialSecurityNumberContact: String,

    //coordinats of person that pays

    //child information

    //emergency contacts
    emergencyContacts: [{
        firstName: String,
        lastName: String,
        phone: String
    }],

    extraInfo: String

});

module.exports = mongoose.model('Registration', RegistrationSchema);

      

        
        
        
      

    

Problem and Solution: The problem was that the client sent the _id = null attribute and therefore MongoDB / Mongoose did not update the id.