How can I disable a form's default validation functions?

Question

I have created my own validate handler:

/**
 * Validate handler.
 */
function my_module_validate($form, &$form_state) {
  $values = $form_state['values'];
  if ($values['type'] == 'line') {
    form_set_error('type', t('MY VALIDATION.'));
  }
}

which is called from a button element:

'preview' => array(
  '#type' => 'button',
  '#value' => t('Preview'),
  '#validate' => array('my_module_validate'),
  '#weight' => 8,
),

which produces this result on submission of an empty form:

The only validation function that I want to run is my own, from my own handler - the last error message - yet all the default validation functions run as well. How do I disable these?

Answer 1

As per function form_set_error: "If #limit_validation_errors is set on a clicked button, the button must also define a #submit property (may be set to an empty array)." So your preview button should be:

'preview' => array(
  '#type' => 'button',
  '#value' => t('Preview'),
  '#limit_validation_errors' => array(array('map')),
  '#submit' => array(),
),

Answer 2

The FAPI allows you to do this without altering the $_SESSION messages array by using #limit_validation_errors.

/**
 * Implements hook_form_alter().
 */
function my_module_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'my_form_id') {
    $form['my_textfield'] = array(
      '#type' => 'textfield',
      '#title' => t('Some title'),
      '#required' => TRUE,
      '#element_validate' => array('my_element_validate'),
    );
    $form['preview'] = array(
      '#type' => 'button',
      '#value' => t('Preview'),
      '#limit_validation_errors' => array(array('my_textfield')),
    );
  }
}

/**
 * My textfield element validate handler.
 */
function my_element_validate($element, &$form_state, $form) {
  // Check the value here.
  if ($element['#value'] == '123') {
    form_error($element, t('123 not allowed!'));
  }
}

Answer 3

I have found a way that works:

$form_required_marker = array('#theme' => 'form_required_marker');
$required = ' ' . drupal_render($form_required_marker);

'map' => array(
  '#type' => 'select',
  '#title' => t('Map') . $required,
  // '#required' => TRUE,
  '#options' => array(
    '' => t('- Select -'),
    'map1' => t('Map 1'),
    'map2' => t('Map 2'),
  ),
),

...then specify a custom validation handler with #validate.

Answer 4

You see different validation error, because your validation callback is called after the error happened. One solution is to call form_clear_error() to clear previous errors and set the new one. Or unset specific element validation error in your element validate callback, e.g.

/**
 * Implements callback for #element_validate Form API.
 */
function my_module_map_validate($element, &$form_state, $form) {
  if (empty($element['#value'])) {
    // Clear previous validation error for this element.
    $errors = &drupal_static('form_set_error', array());
    $err_key = $element['#field_name'] . '][' . LANGUAGE_NONE;
    if (array_key_exists($err_key, $errors)) {
      unset($errors[$err_key]);
    }
    form_error($element, t('xyz'));
    return;
  }
}

Answer 5

I've part solved the problem by using this custom function - but it's not perfect.

It works perfectly on first valiadtion failure, but if I create another validation failure, I get a blank error message and then this error:

Notice: Undefined offset: 0 in theme_status_messages().

Code:

/**
 * Validate handler.
 */
function my_module_validate($form, &$form_state) {
  if ($type = $form_state['values']['type']) {
    switch ($type) {
      case 'map':
        $names = array(
          'line_sub_type',
          'margin_top',
          'margin_right',
          'margin_bottom',
          'margin_left',
          'x_axis_label',
          'y_axis_label',
          'date_time_format',
        );
        break;
      case 'line':
        $names = array(
          'map',
          'land_color',
          'boundary_width',
          'color_key',
          'lighter_end',
          'darker_end',
          'units_format',
        );
        break;
      }  
    foreach ($names as $name) {
      my_module_form_unset_error($name);
    }
  }
}

/**
 * Clear a form element error.
 */
function my_module_form_unset_error($name) {
  $errors = &drupal_static('form_set_error', array());
  $removed_messages = array();
  if (isset($errors[$name])) {
    $removed_messages[] = $errors[$name];
    unset($errors[$name]);
  }
  $_SESSION['messages']['error'] = array_diff($_SESSION['messages']['error'], $removed_messages);
  if (empty($_SESSION['messages']['error'])) {
    unset ($_SESSION['messages']['error']);
  }
}

Answer 6

In hook_form_alter() function, you can unset the default validation rules and then specify your validation function as validate handler

function mymodule_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'YOUR FORM ID') {
    unset($form['#validate']);
    $form['#validate'] = array('my_module_validate');
  }
}

Please note that this change will completely remove the form validations from all the fields and you need to handle the validation of all the fields individually.