lithium\data\model\Relationship::_strategies PHP Method

    protected function _strategies()
    {
        return array(static::LINK_EMBEDDED => function ($object, $relationship) {
            $fieldName = $relationship->fieldName();
            return $object->{$fieldName};
        }, static::LINK_CONTAINED => function ($object, $relationship) {
            $isArray = $relationship->type() === "hasMany";
            return $isArray ? $object->parent()->parent() : $object->parent();
        }, static::LINK_KEY => function ($object, $relationship, $options) {
            $model = $relationship->to();
            if (!($query = $relationship->query($object))) {
                return;
            }
            $method = $relationship->type() === "hasMany" ? 'all' : 'first';
            return $model::$method(Set::merge((array) $query, (array) $options));
        }, static::LINK_KEY_LIST => function ($object, $relationship, $options) {
            $model = $relationship->to();
            $query = $relationship->query($object);
            return $model::all(Set::merge($query, $options));
        });
    }