One to Many mapping in mongoose, How to receive and process?

The problem I have is a One to many mapping with mongoose(Mongodb). The one is the Order(buyer data) and the many is the Items(price,quantity,etc).

1) How I should create the Schema for the the Order and items, like should I put the items in an array in the order?

2) Would all the data be in one post function?

I herd you can use ObjectId to link the many to one but I am not sure how to.

Since an Order sounds like it will have a relative small number of items, the simplest thing would probably be just a list of item Ids:

var OrderSchema = new mongoose.Schema({
    items: [{type: mongoose.Schema.Types.ObjectId, ref: 'Item'}]
});

var ItemSchema = new mongoose.Schema({
    price: Number,
    quantity: Number
});

Most UIs would not build an entire order in a single POST function, so it's probably best to allow creating an order and then separately adding items to it via order.items.push(itemId).