Question

Hi I am using CodeIgniter with DataMapper and really need some help defining relationship in a model class (DataMapper Model Class)

How would I write the model relation for this. Slightly confused about the Self relation, i.e menu item and sub menu

Menu has many submenus and submenus can have one or more sub-submenus

Class: navigation
Table: Navigation
[id] [parent_id] [Name] ..

Thanks

Answer 1

This is a one-to-many relation (an item has one parent, a parent can have many items).

So your model would look like:

class Menu extends DataMapper {

    public $has_one = array(
        'parent' => array(
            'class' => 'menu',
        ),
    );

    public $has_many = array(
        'menu' => array(
            'class' => 'menu',
                'other_field' => 'parent',
        ),
    );

}

This will allow you do do:

// assume your tree root has parent id 0
$root = new Menu();
$root->where('parent_id', 0)->get();

// get the first level menu from the root
$submenu = $root->menu->get();

// get the parent from the first submenu entry (should be root again)
$rootagain = $submenu->parent->get();

Note that (as I already replied on the CI forum) this is not a very optimal solution, as a tree can be several levels of nesting, with this setup it means having to iterate as you can only retrieve one level at the time, and for a single parent. This will become a nightmare for any size tree.

Check out the nestedsets extension, which will allow you to build nested sets tree in a table, and adds the methods to Datamapper to manipulate those sets (like working with parents, children, syblings, inserting new records at specific locations in the tree, etc).