lib/components/types/Relationship.php
public static function getOne(Item $parent, Item $child, $options = [])
    {
        $key = md5($parent->systemId . "." . $child->systemId);
        if (isset(self::$_relationships[$key])) {
            self::$_relationships[$key]->mergeOptions($options);
        } else {
            self::$_relationships[$key] = new Relationship($parent, $child, $options);
        }

        return self::$_relationships[$key];
    }
public static function getOne(Item $parent, Item $child, $options = [])
    {
        $key = md5($parent->systemId . "." . $child->systemId);
        if (isset(self::$_relationships[$key])) {
            self::$_relationships[$key]->mergeOptions($options);
        } else {
            self::$_relationships[$key] = new Relationship($parent, $child, $options);
        }

        return self::$_relationships[$key];
    }
Get one.

@param cascade\components\types\Item $parent  [[@doctodo param_description:parent]]
@param cascade\components\types\Item $child   [[@doctodo param_description:child]]
@param array                         $options [[@doctodo param_description:options]] [optional]

@return [[@doctodo return_type:getOne]] [[@doctodo return_description:getOne]]