如何使用mongodb在集合中添加另一个字段？

I study mongodb and symfony. I succesfully creating a fields by following this documentation from symfony to mongodb link. If you can see documentation. They have these codes for connecting this documents to mongodb

/ src/Acme/StoreBundle/Document/Product.php
namespace Acme\StoreBundle\Document;

use Doctrine\ODM\MongoDB\Mapping\Annotations as MongoDB;

/**
 * @MongoDB\Document
 */
class Product
{
    /**
     * @MongoDB\Id
     */
    protected $id;

    /**
     * @MongoDB\Field(type="string")
     */
    protected $name;

    /**
     * @MongoDB\Field(type="float")
     */
    protected $price;
}

Is this possible adding another field in Product like category, and an under the category there are another fields like adding category_name and category_date? and how can I generate that document?

Update: I want to create like these flow of fields in my mongodb collections

Product
  - id
  - name
  - price
  - category
      - category_name
      - category_date

MongoDb is a Nosql Database and Not Relational. It just accepts anything in key and value format. so may be you can add more fields like category_name and category_date. by adding the variable.