ActiveRecord and many to many relationship ?

Question

I'm trying to implement the Active Record pattern to a ZF project. I used to work with a similar approch before and it works well.

But my problem now, is about how to handle many-to-many relationship with my models.

Here is an example :

Let's say i've an User model.

<?php
require_once 'MLO/Model/Model.php';

class Model_User extends MLO_Model_Model
{   
    protected $_data = array(
        'id' => NULL,
        'email' => NULL,
        'password' => NULL,
    );
}

No problems.

But what if I add a Group model ?

require_once 'MLO/Model/Model.php';

class Model_Group extends MLO_Model_Model
{   
    protected $_data = array(
        'id' => NULL,
        'name' => NULL,
        'desc' => NULL,
    );
}

and

require_once 'MLO/Model/Collection.php';

class Model_Groups extends MLO_Model_Collection
{   
    protected $_modelClass = 'Model_Group';
}

I have then a mapper which convert results from the db to model object, and vice versa.

My question is, how to handle many-to-many relationship with my models ?

Where should i "store the relationship" ?

Here is some clues i think about :

class Model_User extends MLO_Model_Model
{   
    protected $_data = array(
        'id' => NULL,
        'name' => NULL,
        'desc' => NULL,
        'groups' => NULL,  // where groups will be an instance of the Model_Groups
    );
}

With the same approach, where groups will be an array like :

array(3) {
  [0]=>
  array(3) {
    ["id"]=>
    string(1) "9"
    ["name"]=>
    string(1) "Guest"
    ["desc"]=>
    string(1) "Some desc"
  }
  [1]=>
  array(3) {
    ["id"]=>
    string(1) "64"
    ["name"]=>
    string(1) "Moderator"
    ["desc"]=>
    string(1) "Some desc"
  }
  [2]=>
  array(3) {
    ["id"]=>
    string(1) "5"
    ["name"]=>
    string(1) "Admin"
    ["desc"]=>
    string(1) "Some desc"
  }
}

Another ideas ?

P.S : I'm not trying to handle ACLs or similar things, it's just for example.

Answer 1

Let's translate your problem to post tags - one post have many tags and one tag is used with many posts - it's easily understandable (at least to me):

I would add ['tags'] to Page's $_data as you suggest. And it will be array of adjected tag objects. Analogicaly for Tag I'd add ['pages'] with adjected pages. But I would use lazy loading for that of course.

Answer 2

Zend_Db_Table has this functionality built in! :)

It uses its own concepts of "dependentTables" and "referenceMap" to manage table relationships and can even do CASCADE and DELETE stuff for you if your DB doesn't support referential constraints

Zend_Db_Table Relationships