code: public function toJoinAndKey($path)
      {
  
          if(!$this->isRelatedKey($path)){
              return ['', $path];
          }
  
          $stack = $this->splitPath($path);
  
          $prop = array_pop($stack);
  
          return [implode($this->joinDelimiter, $stack), $prop];
  
      }
docs: {@inheritdoc}
  
  @param string $path Der Name der Eigenschaft
  @return array Sowas: array('join.join','id')