Drupal entity reference get all the parents

get-all-parents.php

//Get all the parent of a book as array
function _book2_hlp_get_book_all_parents_array($entity_id, $table = 'node__field_book2_parent', 
  $parent_field = 'field_book2_parent_target_id', $child_field = 'entity_id', 
  $bundle = 'book2') {
  $output = array();


  $node_relation = 'c.' . $child_field . ' = n.nid';

  //Get all the childrens in sinle fetch, 
  //For each fetch, get further children into recurssive 
  $query = db_select($table, 'c');
  $query->fields('c', array($parent_field, $child_field, 'bundle'));
  $query->addField('n', 'title');
  $query->addField('n', 'status');
  $query->addField('n', 'changed');
  $query->join('node_field_data', 'n', $node_relation);  
  //$query->condition('c.' . $parent_field, 'c.' . $child_field, '!=');
  $query->condition($child_field, $entity_id);
  if($bundle) {
    $query->condition('c.bundle', $bundle);
  }
  $query->condition('c.deleted', 0);
  $result = $query->execute()->fetchAllAssoc($child_field);

  if($result && count($result) && $entity_id) {
    foreach($result as $result) {
      $_pid = $result->{$parent_field};
      $output[$result->{$child_field}] = $result;
      if($result->{$child_field} == $result->{$parent_field}) {
        return $output;
      }
      $_tmp_childs = _book2_hlp_get_book_all_parents_array($_pid, $table, $parent_field, $child_field, $bundle);
      if($_tmp_childs && count($_tmp_childs)) {
        foreach($_tmp_childs as $_tmp_child) {
          $_tmp_pid = $_tmp_child->{$child_field};
          $output[$_tmp_pid] = $_tmp_child;
        }
      }
      //break;
    }
  }
  // Get the top most parent item
  else {
    if(!$entity_id) {
      return FALSE;
    }
    $query2 = db_select('node_field_data', 'n');
    $query2->addField('n', 'title');
    $query2->addField('n', 'status');
    $query2->addField('n', 'changed');
    $query2->addField('n', 'nid', $child_field);
    $query2->condition('nid', $entity_id);

    $result2 = $query2->execute()->fetchAllAssoc($child_field);
    if($result2 && count($result2)) {
      foreach($result2 as $_pid => $result2) {
        $output[$_pid] = $result2;
        $output[$_pid]->field_book2_parent_target_id = 0;
        $output[$_pid]->bundle = $bundle;
      }
    }
  }
  return $output;
}