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<?php
/**
 * Find taxonomy term (by name) limited by parent term.
 * 
 * In many cases you may need to find children in exact term (parent). 
 * Here we do this in efficent way with precise query (not like taxonomy_get_tree()
 * where all the terms loading. 
 * 
 * @param $name
 * @param $parent
 * @param $vid
 *
 * @return array
 * Terms array or empty array if nothing found.
 */
function taxonomy_find_term_by_parent($name, $parent, $vid) {
  $query = db_select('taxonomy_term_data', 't');
  $query->join('taxonomy_term_hierarchy', 'h', 'h.tid = t.tid');
  $result = $query
    ->addTag('translatable')
    ->addTag('taxonomy_term_access')
    ->fields('t')
    ->fields('h', array('parent'))
    ->condition('t.vid', $vid)
    ->condition('t.name', $name)
    ->condition('h.parent', $parent)
    ->orderBy('t.weight')
    ->orderBy('t.name')
    ->execute();
  
  $terms = [];
  
  foreach ($result as $term) {
    $terms[$term->tid] = $term;
  }
  
  return $terms;
}