PHP WordPress Example Nested parent->id mapping

example.php

<?php

/**
 * If WordPress will ever work smoothly with procedures, we want to refactor this.
 * @param $search_term
 * @return array
 */
function example_nested_parent_map_search( $search_term ) {
  global $wpdb;

  $sql = 'SELECT id, 
                   parent_id 
              FROM `your-table`
             WHERE content LIKE "%' . $search_term . '%"';

  $results = $wpdb->get_results( $sql );

  if( empty( $results ) )
    return [];

  $response = [];
  $required_parent_ids = [];

  foreach( $results as $result ) {
    if( !isset( $response[ $result->parent_id ] ) )
      $response[ $result->parent_id ] = [];

    $response[ $result->parent_id ][] = $result->id;

    if( $result->parent_id != 0 )
      $required_parent_ids[] = $result->parent_id;
  }

  if( empty( $required_parent_ids ) )
    return $response;

  while( !empty( $required_parent_ids ) ) {
    $sql = 'SELECT id, 
                     parent_id 
                FROM `your-table`
               WHERE id IN (' . implode( ",", $required_parent_ids ) . ')';

    $results = $wpdb->get_results( $sql );

    if( empty( $results ) )
      return $response;

    $required_parent_ids = [];

    foreach( $results as $result ) {
      if( !isset( $response[ $result->parent_id ] ) )
        $response[ $result->parent_id ] = [];

      $response[ $result->parent_id ][] = $result->id;

      if( $result->parent_id != 0 )
        $required_parent_ids[] = $result->parent_id;
    }
  }

  return $response;
}