public function addRef($link, $callback) : Reference
    {
        return $this->_hasReference($this->_default_seed_addRef, $link, $callback);
    }
public function addRef($link, $callback) : Reference
    {
        return $this->_hasReference($this->_default_seed_addRef, $link, $callback);
    }
public function addRef ( $ link , $ callback ) : Reference { return $ this -> _hasReference ( $ this -> _default_seed_addRef , $ link , $ callback ) ; }
Add generic relation. Provide your own call-back that will
return the model.

@param string         $link     Link
@param array|callable $callback Callback

@throws Exception
@throws \atk4\core\Exception

@return Reference
Add generic relation . Provide your own call - back that will return the model .