Cast Mongoose Document to other similar Model - node.js

Question

So I have the following layout for my app:
UserSchema (contains username and password)
var UserSchema = new mongoose.Schema({
firstName: String,
lastName: String,
email: String,
username: String,
password: String
}, options);
UserSchema.plugin(passportLocalMongoose);
module.exports = mongoose.model("User", UserSchema);
StudentSchema (discriminator() on User) with additional fields
var StudentSchema = new mongoose.Schema({
indexNumber: String,
courses: [{
id: {
type: mongoose.Schema.Types.ObjectId,
ref: "Course"
},
entryDate: {
type: Date,
default: Date.now
}
}]
}, options);
module.exports = User.discriminator("Student", StudentSchema);
TeacherSchema (discriminator() on User) with additional fields
var TeacherSchema = new mongoose.Schema({
degree: String,
courses: [{
type: mongoose.Schema.Types.ObjectId,
ref: "Course"
}]
}, options);
module.exports = User.discriminator("Teacher", TeacherSchema);
I am using passport local-strategy to User.register().
router.post("/register", function(req,res) {
var newUser = new User({
firstName: req.body.firstName,
lastName: req.body.lastName,
email: req.body.email,
username: req.body.username
});
User.register(newUser, req.body.password, function(err, user) {
if(err) throw err;
passport.authenticate("local")(req, res, function() {
req.flash("success", "Welcome " + user.username + ".");
res.redirect("/");
});
});
});
Now all this is under same collection users in db (because of discriminators)
How do I, after an user registers, "promote" him to student or teacher, so I can have those additional fields in his object?

Answer 1

Try setting __t to "Teacher" or "Student" using an update command on the User model. I think the default discriminator key is __t so you need something like:
user.update({$set: {__t: "Student" } }, callback)`
Then you'll need to pull it with the Discriminator again to get your fields:
const Student = User.discriminator("Student", StudentSchema);
Student.findById(id, callback)