Save two referenced documents simultaneously

I've got an stock application where I want to set some details about the stock and then insert all the items of the stock. I want to insert the stock details and the items in two different collection so then I can filter the items. I'm using the MEAN Stack where I've modified the crud module to accept some extra fields and also made the UI for filling the items array.This what I have so far:

scope.stockItems = [];

    $scope.createStockItem = function () {
        $scope.stockItems.push(
            {
                brand: $scope.brand,
                style: $scope.style,
                amount: $scope.amount
            }
        );

        $scope.brand = false;
        $scope.style = false;
        $scope.amount = '';
    };

    // Create new Stock
    $scope.create = function() {
        // Create new Stock object
        var stock = new Stocks ({
            name: this.name,
            details: this.details,
            stockDate: this.stockDate
        });

        // Redirect after save
        stock.$save(function(response) {
            $location.path('stocks/' + response._id);

            // Clear form fields
            $scope.name = '';
        }, function(errorResponse) {
            $scope.error = errorResponse.data.message;
        });
    }; 

The stock model:

var StockSchema = new Schema({
name: {
    type: String,
    default: '',
    required: 'Please fill Stock name',
    trim: true
},
details: {
    type: String,
    default: '',
    required: 'Please fill Stock details'
},
stockDate: Date
created: {
    type: Date,
    default: Date.now
},
user: {
    type: Schema.ObjectId,
    ref: 'User'
}
});

and the method in the server controller:

exports.create = function(req, res) {
var stock = new Stock(req.body);

stock.user = req.user;

stock.save(function(err) {
    if (err) {
        return res.status(400).send({
            message: errorHandler.getErrorMessage(err)
        });
    } else {
        res.jsonp(stock);
    }
});
};

How can I send into the request and save the stockItems also?