Simply add a field to comments

OK, after quite some time, I have finally done this!

Here is how.

Create a new module with the 3 necessary files: yourmodule.info, yourmodule.install & yourmodule.module

Then inside your .info file you will have something like:

; $Id$
name = Your Module
description = Allows you to add a field to the comment form through the drupal form api
core = 6.x
dependencies[] = comment

Your .install file:

/* this module sets up any tables we need for the data we will be storing
   it may be necessary to alter some of the queries to your needs. */
function yourmodule_schema() {
  $schema['yourmodule'] = array(
    'description' => t('...??'),
    'fields' => array(
      'id' => array(
        'type' => 'serial'
        // zerofill auto_increment
      ),
      'xid' => array(
        'type' => 'int',
        'unsigned' => TRUE
        // default NULL
        // zerofill
      ),
      'type' => array(
        'type' => 'varchar',
        'length' => 16
        // enum('node', 'comment')
        // not null
        // null check
      ),
      'val' => array(
        'type' => 'varchar',
        'length' => 999
        // default NULL
      ),
    ),
    'primary key' => array('id')
  );
  return $schema;
}

function yourmodule_install() {
  drupal_install_schema('yourmodule', 'yourmodule');
}

function yourmodule_uninstall() {
  drupal_uninstall_schema('yourmodule', 'yourmodule');
}

Then in your .module file:

/* Add our new field to the content types and/or comments */
function yourmodule_form_alter(&$form, $form_state, $form_id) { // form override
  if ($form_id == 'forum_node_form') { // add field to forum content type
    unset($form['taxonomy']['5']['#options'][4]);
    $form['cb2vsn'] = array(
    '#type' => 'hidden', // I have used hidden fields here, because this is what I needed, you may also need to change this to suit your needs
    '#id' => t('edit-field-cb2vsn-0-value'),
    '#default_value' => '',
    );
  }
  if ($form_id == 'comment_form') { // add field to comment content type
    $form['cb2vsn'] = array(
    '#type' => 'hidden', // I have used hidden fields here, because this is what I needed, you may also need to change this to suit your needs
    '#id' => t('edit-field-cb2vsn-0-value'),
    '#default_value' => '',
    );
  }
}

/* set up permissions */
function yourmodule_perm() {
  return array('view your field');
}

/* operations for handling the values inserted into a node's form */
function yourmodule_nodeapi(&$node, $op) {
  switch ($op) {
    case 'insert': // insert in the database
      $cb2sig = $node->cb2vsn; // here is my field as created in the last form_alter()
      db_query("INSERT INTO {yourmodule} (xid, type, val) VALUES(%d, '%s', '%s')", $node->nid, 'node', $cb2sig);
      break;
    case 'view': // get it from the database for display
      if (user_access('view your field')) {
        $result = db_fetch_object(db_query("SELECT val FROM {yourmodule} WHERE type='node' AND xid = %d", $node->nid));
        if ($result->val) {
          $node->yourfield = $result->val;
        }
      }
      break;
  }
}

/* operations for handling the values inserted into a comment's form */
function yourmodule_comment(&$comment, $op) {
  switch ($op) {
    case 'insert': // insert in the database
      $cb2sig = $comment['cb2vsn']; // here is my field as created in the last form_alter()
      db_query("INSERT INTO {yourmodule} (xid, type, val) VALUES(%d, '%s', '%s')", $comment['cid'], 'comment', $cb2sig);
      break;
    case 'view': // get it from the database for display
      if (user_access('view your field')) {
        $result = db_fetch_object(db_query("SELECT val FROM {yourmodule} WHERE type='comment' AND xid = %d", $comment->cid));
        $comment->yourfield = $result->val;
      }
      break;
  }
}

The last thing you have to do is to add to your template files: $node->yourfield or $comment->yourfield to display the field where you may need it in the comments or node.

I hope someone gets some use out of this, because I had to search really hard on it. I ended up pulling most of my code out of the user agent module.