function __construct(Model $parent, Model $related, $pivot_builder, $foreign_key, $other_key)
 {
     parent::__construct($parent, $related);
     $this->pivot_builder = $pivot_builder;
     $this->foreign_key = $foreign_key;
     $this->other_key = $other_key;
 }
 function __construct(Model $parent, Model $related, $foreign_key)
 {
     parent::__construct($parent, $related);
     $this->foreign_key = $foreign_key;
 }
 function setRelation($name, Relations\Relation $relation)
 {
     $this->relations[$name] = $relation->relate($this);
 }