Datamapper DB Pattern With ZF: Managing a Relational Database

I am creating an application using Zend Framework and I want to use the data mapper design pattern for managing my database. What I don't understand is how to use the pattern with a relational database.

Suppose I have a table containing posts with columns id, title, text and author. I could use the following classes to manage this:

class Application_Model_DbTable_Posts extends Zend_Db_Table_Ab开发者_如何学Cstract
{
    $_name = 'posts';
}

class Application_Model_PostMapper
{
    public function setDbTable($dbTable);
    public function getDbTable();
    public function save($post);
    public function find($id);
    public function fetchAll();
}

class Application_Model_Post
{
    protected $_id;
    protected $_title;
    protected $_text;
    protected $_author;

    public function __set($name, $value);
    public function __get($name);
}

Now, suppose I wanted to create a one-to-many relationship -- comments, for example -- how would I do this? And a many-to-many relationship? -- or would that be done the same was as a one-to-many?

Please provide code samples in your answers if possible, in order to help me understand.

Generally speaking, if your Application_Model_Post models has a collection of Application_Model_Comments, you would set up appropriate Db_Table and Mapper for comments, and extend your Post model in some way, to enable getting comments for a particular post.

You might decide to inject the CommentMapper into your Post model:

class Application_Model_Post {
    protected $_commentMapper;

    function __construct($commentMapper){
        $this->_commentMapper = $commentMapper;
    }

    function getComments(){
        return $this->_commentMapper->findByPostId($this->getId());
    }
}

Note that your Post model still knows nothing of the persistence layer. All the details about loading comments is abstracted away in your CommentMapper.