In the following example we have one database table called 'entity'. Users and groups are both entities and they share the same database table.

The entity table has a column called 'type' which tells whether an entity is a group or a user. Then we decide that users are type 1 and groups type 2.

The only thing we have to do is to create 3 records (the same as before) and add call the Doctrine_Table::setInheritanceMap() method inside the setUp() method.

<code type="php">
class Entity extends Doctrine_Record { 
    public function setTableDefinition() {
        $this->hasColumn("name","string",30);
        $this->hasColumn("username","string",20);
        $this->hasColumn("password","string",16);
        $this->hasColumn("created","integer",11);
        
        // this column is used for column 
        // aggregation inheritance
        $this->hasColumn("type", "integer", 11);
    }
}

class User extends Entity {
    public function setUp() {
        $this->setInheritanceMap(array("type"=>1));
    }
}

class Group extends Entity {
    public function setUp() {
        $this->setInheritanceMap(array("type"=>2));
    }
}
</code>

If we want to be able to fetch a record from the Entity table and automatically get a User record if the Entity we fetched is a user we have to do set the subclasses option in the parent class. The adjusted example:

<code type="php">
class Entity extends Doctrine_Record { 
    public function setTableDefinition() {
        $this->hasColumn("name","string",30);
        $this->hasColumn("username","string",20);
        $this->hasColumn("password","string",16);
        $this->hasColumn("created","integer",11);
        
        // this column is used for column 
        // aggregation inheritance
        $this->hasColumn("type", "integer", 11);
				$this->option("subclasses", array("User", "Group");
    }
}

class User extends Entity {
    public function setUp() {
        $this->setInheritanceMap(array("type"=>1));
    }
}

class Group extends Entity {
    public function setUp() {
        $this->setInheritanceMap(array("type"=>2));
    }
}
</code>

We can then do the following given the previous table mapping.

<code type="php">
$user = new User();
$user->name="Bjarte S. Karlsen";
$user->username="meus";
$user->password="rat";
$user->save();

$group = new Group();
$group->name="Users";
$group->username="users";
$group->password="password";
$group->save();

$q = Doctrine_Query();
$user = $q->from("Entity")->where("id=?")->execute(array($user->id))->getFirst();

$q = Doctrine_Query();
$group = $q->from("Entity")->where("id=?")->execute(array($group->id))->getFirst();
</code>

The user object is here an instance of User while the group object is an instance of Group.