I have a Drupal 8 User registration form that has several text fields to gather information about the user.

I'd like to write a custom hook that examines the values in those fields and then either proceeds with the registration or 'cancels' it, like perhaps redirecting to a static page or displaying some static content.

What are the hooks I need to make this happen? Do I alter the form? Or do I hook an entity_presave function?

What do I need to do to cancel the default form processing or default entity presave/save routines?


1 Answer 1


Forms have a validate and submit function(s). Submit never runs unless all validation passes.

So all you have to do is add a custom validation

 * Implements hook_form_FORM_ID_alter
function mymodule_form_user_register_form_alter(&$form, FormStateInterface $form_state) {

  $form['#validate'][] = 'mymodule_registration_validate';


 * Custom Validation
function mymodule_registration_validate(&$form, FormStateInterface $form_state) {

  $field_name = $form_state->getValue('field_name'); // Gets the value entered by the user
  // Note: depending on your field type & settings sometimes this value is an
  // array, so you may have to keep drilling down.
  if($field_name != 'Hello World') { // perform check
    $message = t('Only Hello World is allowed'); // message to display
    $form_state->setErrorByName('field_name', $message); // set error


$form_state->setErrorByName will display an error message and highlight the offending field in red.

If you want to redirect use $form_state->setRedirectUrl($url);

  • 1
    I'm tempted to try to post another answer using the DEV version of the Rules module ... nevertheless: this one is not so bad either ... Jan 20, 2019 at 13:25
  • I initially thought of this, but what if I wanted to register the user but keep them blocked? In this case I think I wouldn't want to do it in validation hooks, because the validation is meant to permit or deny further form processing, right?
    – meecect
    Jan 28, 2019 at 16:01
  • @meecect Correct. That would require a totally diff aproach.
    – No Sssweat
    Jan 28, 2019 at 16:13

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