public function hasOne($link, $defaults = []) : Reference
    {
        return $this->_hasReference($this->_default_seed_hasOne, $link, $defaults);
    }
public function hasOne($link, $defaults = []) : Reference
    {
        return $this->_hasReference($this->_default_seed_hasOne, $link, $defaults);
    }
public function hasOne ( $ link , $ defaults = [ ] ) : Reference { return $ this -> _hasReference ( $ this -> _default_seed_hasOne , $ link , $ defaults ) ; }
Add hasOne field.

@param string $link
@param array  $defaults

@throws Exception
@throws \atk4\core\Exception

@return Reference\HasOne
Add hasOne field .