doctrine2/manual/codes/Object relational mapping - Relations - Join table associations - Many-to-Many.php

<?php
class User extends Doctrine_Record { 
    public function setUp() {
        $this->hasMany('Group','Groupuser.group_id');
    }
    public function setTableDefinition() {
        $this->hasColumn('name','string',30);
    }
}

class Group extends Doctrine_Record {
    public function setUp() {
        $this->hasMany('User','Groupuser.user_id');
    }
    public function setTableDefinition() {
        $this->hasColumn('name','string',30);
    }
}

class Groupuser extends Doctrine_Record { 
    public function setTableDefinition() {
        $this->hasColumn('user_id','integer');
        $this->hasColumn('group_id','integer');
    }
}


$user = new User();

// add two groups
$user->Group[0]->name = 'First Group';

$user->Group[1]->name = 'Second Group';

// save changes into database
$user->save();

// deleting the associations between user and groups it belongs to

$user->Groupuser->delete();

$groups = new Doctrine_Collection($conn->getTable('Group'));

$groups[0]->name = 'Third Group';

$groups[1]->name = 'Fourth Group';

$user->Group[2] = $groups[0];
// $user will now have 3 groups

$user->Group = $groups;
// $user will now have two groups 'Third Group' and 'Fourth Group'

?>