Accessing more than one model deep relationships in Lithium

Is it possible to access more than one model deep in a relationship in Lithium?

For example, I have a User model:

class Users extends \lithium\data\Model {
    public $validates = array();
    public $belongsTo = array("City");
}

and I have a City model:

class Cities extends \lithium\data\Model {
    public $validates = array();
    public $belongsTo = array("State");
}

and a State model, and so on.

If I'm querying for a User, with something similar to Users::first(), is it possible to get all the relationships included with the results? I know I can do Users::first(array('with' => 'City')) but I'd like to have each City return its State model, too, so I can access it like this:

$user->city->state->field

Right now I can only get it to go one deep ($user->city) and I'd have to requery again, which seems inefficient.

I am guessing you are using SQL?

Lithium is mainly designed for noSQL db´s, so recursiveness / multi joins are not a design goal.

You could set up a native sql join query and cast it on a model.
query the city with Users and State as joins.
you could setup a db based join view and li3 is using it as a seperate model.
you probably should split your planned recursive call into more than one db requests.

Think about the quotient of n Cities to m States. => fetch the user with city and then the state by the state id. => pass that as two keys or embed the state info. This would be acceptable for Users::all() queries aswell.

Example using Lithiums util\Set Class:

use \lithium\util\Set;
$users = Users::all(..conditions..);
$state_ids = array_flip(array_flip(Set::extract($users->data(), '/city/state_id')));
$stateList = States::find('list',array(
    'conditions' => array(
        'id' => $state_ids
    ),
));

Using a recent master you can use the following nested notation:

Users::all( array( 
    'with' => array(
        'Cities.States'
    ) 
));

It will do the JOINs for you.

You can set up relationships in this way, but you have to use a more verbose relationship definition. Have a look at the data that gets passed when constructing a Relationship for details about the options you can use.

class Users extends \lithium\data\Model {
    public $belongsTo = array(
        "Cities" => array(
            "to" => "app\models\Cities",
            "key" => "city_id",
        ),
        "States" => array(
            "from" => "app\models\Cities",
            "to" => "app\models\States",
            "key" => array(
                "state_id" => "id", // field in "from" model => field in "to" model
            ),
        ),
    );
}

class Cities extends \lithium\data\Model {
    public $belongsTo = array(
        "States" => array(
            "to" => "app\models\States",
            "key" => "state_id",
        ),
    );
}

class States extends \lithium\data\Model {
    protected $_meta = array(
        'key' => 'id',  // notice that this matches the value 
                        // in the key in the Users.States relationship
    );
}

When using the States relationship on Users, be sure to always include the Cities relationship in the same query. For example:

Users::all( array( 
    'with' => array(
        'Cities', 
        'States'
    ) 
) );

I have never tried this using belongsTo relationships, but I have it working using hasMany relationships in the same way.

来源：https://stackoverflow.com/questions/9836392/accessing-more-than-one-model-deep-relationships-in-lithium

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