Mongoose one-to-many - not quite sure how to implement it - node.js

Question

I'm relatively new to Mongoose (2 days at it) and I want to make a one-to-many relationship, as in one person can come from one country, one country has many people.
So, this is what I've got:
var userSchema = new Schema({
name: String,
username: {
type: String,
required: true,
unique: true
},
password: {
type: String,
required: true
},
country: {
type: Schema.Types.ObjectId,
ref: 'Country'
}
});
var User = mongoose.model('Person', userSchema);
var countrySchema = new Schema({
name: {
type: String,
required: true,
unique: true
},
created_at: Date,
updated_at: Date,
people: [{
type: Number,
ref: 'User'
}]
});
var Country = mongoose.model('Country', countrySchema);
var UK = new Country({
name: 'UK'
});
usa.save(function(err) {
var user = new User({
username: 'James',
password: 'Bond',
country: UK._id
});
user.save(function(err) {
});
});
Now I have two questions: 1) I've seen that ref can sometimes be an ObjectId or just a number - what's the differences? 2) when saving the data, in my case, I saved country to a person (by _id), how do I save a person to a country? Should I update the instance of the model?
Thanks
UPDATE:
since this question has been marked as a duplicate, let me rephrase the question: consider the official example in this link: http://mongoosejs.com/docs/populate.html
The idea is that one person has many stories, and one story has one author (person). So, the saving would be as follows:
var aaron = new Person({ _id: 0, name: 'Aaron', age: 100 });
aaron.save(function (err) {
if (err) return handleError(err);
var story1 = new Story({
title: "Once upon a timex.",
_creator: aaron._id // assign the _id from the person
});
story1.save(function (err) {
if (err) return handleError(err);
// thats it!
});
});
That's from the official documentation - my question is, where or how do we save story1 to the Author? Author is created before the Story, so, shouldn't the Author be updated with story1._id???
UPDATE 2:
I figured out that if I use only type: Schema.Types.ObjectId and never type: Number, that I can do just this:
var aaron = new Person({ _id: 0, name: 'Aaron', age: 100 });
var story1 = new Story({
title: "Once upon a timex.",
_creator: aaron._id // assign the _id from the person
});
aaron.stories.push(story1._id);
aaron.save(function (err) {
if (err) return handleError(err);
});
story1.save(function (err) {
if (err) return handleError(err);
// thats it!
});
This actually works in a dummy example... are there any problems if there were too many posts in a request that IDs could have get lost/duplicated? What is the shortcoming of this approach?

Answer 1

1) I've seen that ref can sometimes be an ObjectId or just a number - what's the differences?
Please refer to this question Why do they use an ObjectId and a Number in the Mongoose Population example?
where or how do we save story1 to the Author
aaron.save(function (err) {
if (err) return handleError(err);
var story1 = new Story({
title: "Once upon a timex.",
_creator: aaron._id // assign the _id from the person
});
story1.save(function (err) {
if (err) return handleError(err);
// save id of story1 into person here, also you should use `update` operation with `$push` operator.
aaron.stories.push(story1._id);
aaron.save(function(err){
if (err)
handleError(err);
else
console.log('save person successfully...');
})
});
});
The results
> db.stories.find()
{ "_id" : ObjectId("56f72f633cf1e6f00159d5e7"), "title" : "Once upon a timex.", "_creator" : 0, "fans" : [ ], "__v" : 0 }
> db.people.find()
{ "_id" : 0, "name" : "Aaron", "age" : 100, "stories" : [ ObjectId("56f72f633cf1e6f00159d5e7") ], "__v" : 1 }