/**
  * Find model by id.
  *
  * @param mixed $id
  * @return ElasticsearchModel|null
  */
 public function find($id)
 {
     $child = $this->childClassName;
     $model = $child::findWithParentId($id, $this->parent->getId());
     if ($model) {
         $model->setParent($this->parent);
     }
     return $model;
 }
 /**
  * Set parent document.
  *
  * @param ElasticsearchModel $parent
  */
 public function setParent(ElasticsearchModel $parent)
 {
     $this->_parent = $parent;
     $this->setParentId($parent->getId());
 }