taxonomy_get_children always returns nothing for $tid = 0

On the other hand, there are no term with tid = 0, lowering priority. It makes sense to fix this.

A parent tid of 0 means that there is no parent [it should rather be NULL, but that's the way it currently works].

Maybe taxonomy_get_tree($vid, 0, 1); ?

One parameter to taxonomy get tree is the number of levels you want to retrieve...

Well it should be pretty easy to make a patch for it. See http://drupal.org/patch/create

This isn't a major bug, just a nice to have. I'm not really convinced that 0 should be treated as a valid tid but it won't necessarily make anything worse.

Subscribing.

When trying to traverse a taxonomy tree recursively, it would be nice not to have to call a different function to get the top level terms.

Patch attached. Using isset() as proposed in the OP doesn't really make sense since $tid is a mandatory function argument and thus always set.

Here is a reroll from #1136408: taxonomy_get_children should support getting top level terms.

@jcisio: thanks for rerolling my patch from the other issue to D8. My patch also works when the top level terms are queried for different vid's: the static cache will distinguish these cases and store them separately...

- I think we should integrate the documentation change from #13.
- Some tests should be welcome.

@BartK (#12): +1
@Catch (#10): What I don't get is why there was/is a parameter $vid at all, if $tid = 0 would not be allowed. Because tids are already unique and thus unambiguously define the vid, unless tid = 0.

taxonomy_get_children got renamed to taxonomy_term_load_children in #1377628: taxonomy_get_term_by_name() should be taxonomy_term_load_multiple_by_name(). And taxonomy_term_load_children is deprecated in #1976298: Move taxonomy_get_tree() and associated functions to Taxonomy storage, deprecate procedural wrappers. but the existing code includes the fix from #15

  /**
   * {@inheritdoc}
   */
  public function loadChildren($tid, $vid = NULL) {
    if (!isset($this->children[$tid])) {
      $children = array();
      $query = $this->database->select('taxonomy_term_field_data', 't');
      $query->join('taxonomy_term_hierarchy', 'h', 'h.tid = t.tid');
      $query->addField('t', 'tid');
      $query->condition('h.parent', $tid);
      if ($vid) {
        $query->condition('t.vid', $vid);
      }
      $query->condition('t.default_langcode', 1);
      $query->addTag('term_access');
      $query->orderBy('t.weight');
      $query->orderBy('t.name');
      if ($ids = $query->execute()->fetchCol()) {
        $children = $this->loadMultiple($ids);
      }
      $this->children[$tid] = $children;
    }
    return $this->children[$tid];
  }

But this issue is still valid for D7 so moving it to 7.x. Because it is fixed in 8.x it's a task in 7.x

doh!!