Problem with node revisions and taxonomy terms

Question

I have a content type with a number of fields including a checkbox which allows you to select one or more taxonomy terms. If I create a new version of a node, all the previous taxonomy terms are automatically included in the new node version. I can see this in the database table "field_revision_field_catagories" (catagories is my checkbox field).

If I update the checkbox field with fewer terms checked, Drupal will not remove the existing ones. For example:

Node Version 1 has taxonomy terms 1,3,5 7 checked and 4 corresponding records in the database table.

• I use node_load() to get Version one from the database.
• I update the node using a Form API form and change the checkbox to select 2 (uncheck 1,3,5,7)
• save the node with node_save().

The database now has Version 2 with taxonomy records 2,3,5,7. It updated the first record, changing it from 1 to 2. The other 3 records are still there, however and need to be removed for my logic to work.

I guess I can use SQL to delete the records (or just delete them all after node_load()), but will that create other problems? Is there a Drupal function I can use instead of SQL?

Thanks.

Answer 1

I figured it out. unset() is the answer. Here is my code:

        $loop = 0;  

    $termarr = $form_state['values']['catagories'];
    // drupal_set_message('Termarray '. print_r($termarr,1) .'');
    foreach ($termarr as $term) {
      if ($term > 0) {
        $node->field_catagories['und'][$loop] = array('tid' => $term);
      } else {
        unset($node->field_catagories['und'][$loop]);
      }
      $loop++;
    }

This took way longer than it should have. I wish Drupal had better documentation although trial and error for days does have some benefits... :-(