Last updated May 16, 2019

When a form is submitted you'll need to check the data input by the user to ensure that it matches certain constraints, and to raise errors when necessary. Is the email address in the proper format? Is the title field long enough? Does the ASIN ID entered match a valid Amazon product? This process is called validation and is handled by a combination of the validateForm() method of a form controller, and validation callbacks.

In this tutorial we'll:

  • Explain the use case for both the validateForm() method of a form controller, and validation callbacks
  • Discuss additional uses for validation handlers beyond just checking the length of a text field, or format of a phone number field

By the end of this tutorial you should know how to start adding custom validation logic to any form in Drupal.