Updating a term reference programatically

Question

I've written a module that - among other things - automatically categorizes uploaded files based on their file extension. The idea is simple: the module programatically sets up a taxonomy and automatically adds new terms to it whenever it stumbles upon a new file extension (i.e. pdf, .doc, .jpg etc.).

I cannot get it to work, however. The taxonomy terms are succesfully added to the taxonomy and I can go and investigate them in the admin interface, but the term reference between the node and the term is never saved to the database. I use $node->computed_file_extension[$node->language][0] = $term->tidto save the reference and I'm pretty sure that I've done this with sucess in the past.

I'm actually a bit confused about using 'und' or $node-language. I suppose $node->langugage is the more universal of the two, but it seems it does not always work - in this case I've tried both without success.

When I inspect my node object I can see that the reference is on the node object, but there are no records added to the table taxonomy_index in the DB when node_save() is triggered.

I'm triggering this function on either node update, node insert or node delete and only if changes have been made to the field where I store the uploaded file (i.e. a file has been added or removed).

function _uvp_fields_update_field_file_extension($node) {

// Load the vocabulary called 'file extensions'.
  $vocabulary = taxonomy_vocabulary_machine_name_load('file_extensions');

  if (!empty($vocabulary)) {
    if (!empty($node->field_file['und'][0]['fid'])) {
      $file = file_load($node->field_file['und'][0]['fid']);

// Split the filename and grab the last part to get the file extension.
      $extension = array_pop(explode('.', $file->filename));

      $term = current(taxonomy_get_term_by_name($extension));

// If there is not already a taxonomy term with the given extension, create it.
      if (empty($term)) {

// Build taxonomy term object.
        $term = (object) array(
          'vid'  => $vocabulary->vid,
          'name' => $extension,
        );

// Save the taxonomy term.
        taxonomy_term_save($term);
      }

// Add taxonomy term reference.
      $node->computed_file_extension[$node->language][0] = $term->tid;
//$node->computed_file_extension['und'][0] = $term->tid;

    }
    else {

// If the file has been removed, remove the tag.
      unset($node->computed_file_extension['und'][0]);
    }

// Save the node.
    node_save($node);

    return TRUE;

  }
  else {

    watchdog('uvp_fields', 'The vocabulary "file_extensions" does not exists.');

    return FALSE;
  }
}

Answer 1

You're one level off; this:

$node->computed_file_extension[$node->language][0] = $term->tid;

Needs to be this:

$node->computed_file_extension[$node->language][0]['tid'] = $term->tid;

Without specifying the field column (tid in this case), Drupal doesn't know which DB field the data should be stored in.