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/**
 * Getting term depth.
 *
 * @return int
 *   Depth value.
 */
function term_depth($tid) {
  $query = "SELECT parent FROM {taxonomy_term_hierarchy} WHERE tid = :tid";
  $parent = db_query($query, array(':tid' => $tid))->fetchField();
  return ($parent == 0) ? 1 : 1 + term_depth($parent);
}