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Dec 03 2010
Dec 03

Although CCK automatically does some basic validation on your fields that you add to your Drupal content types, there are some cases where you'd like to do some additional validation for your site. One use case that I ran into recently was a basic text field that was being used to house hyperlinks for one of my websites. The text field had already been in place and working perfectly for months. Rather than do something drastic like replacing the field altogether with a field provided by the "Link" module, I decided to do a hook_form_alter to add in my own custom validation function.

Basically you just create a custom module for your site called "form_alterations" or whatever you like. Here's the code for adding in this sort of functionality:

* Implementation of hook_form_alter().
function form_alterations_form_alter(&$form, &$form_state, $form_id) {
  switch (
$form_id) {
// Simply add an additional link validate handler.
$first = array_shift($form['#validate']);
array_unshift($form['#validate'], $first, 'form_alterations_link_validate');
* FAPI #validate handler. Make sure the hyperlink they used is correctly formatted.
function form_alterations_link_validate($form, &$form_state) {
  if (!empty(
$form_state['values']['field_web_address'][0]['value']) && !strstr($form_state['values']['field_web_address'][0]['value'], 'http://')) {
form_set_error('field_web_address', t('Please enter a full web address starting with "http://".'));

hook_form_alter allows you to use the Drupal Form API to make changes to existing forms. In the code above, I'm adding in a call to my custom function called "form_alterations_link_validate" after the basic CCK validation takes place. Then, within the function itself, I check to make sure that the user entered a value and that it contains "http://" at the beginning of what was entered. If you use the code above, please just be sure to change the line with "case 'announcement_node_form':" so that it modifies the form for your node type. My node type was called "announcement".

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