gistfile1.js

Y.Order = Y.Base.create('order', Y.Model, [Y.ModelSync.REST], {
    root: '/orders/',
    
    initializer: function () {
        this._products = new Y.ModelList({model: 'Product'});
    },
    
    _getProducts: function () {
        return this._products;
    },
    
    _setProducts: function (products) {
        return this._products.reset(products);
    }
}, {
    ATTRS: {
        products: {
            getter: '_getProducts',
            setter: '_setProducts'
        }
    }
});

Y.Product = Y.Base.create('product', Y.Model, [], {}, {
    ATTRS: {
        name: {
            value    : null,
            validator: Y.Lang.isString
        },
        
        price: {
            value    : 0,
            validator: Y.Lang.isNumber
        }
    }
});

var myOrder = new Y.Order({
    products: [
        {name: 'Pen',   price: 1.00},
        {name: 'Paper', price: 1.50}
    ]
});

myOrder.save();