Drupal’s Form API provides many powerful features for validating user submitted data and ensuring that your forms are secure, and the data they collect is accurate.
This course covers the basics of form validation, including how to implement validation logic within form controllers, add validation callbacks to existing forms, and validate individual form elements. You will also learn how to handle errors and ensure that user input meets specific constraints before processing it further. By the end of the course, you will be able to create robust and secure forms that provide a seamless user experience while ensuring data integrity.
Key topics
- Overview of form validation in Drupal
- Implementing validation logic in form controllers
- Adding validation callbacks to existing forms using hook_form_alter()
- Validating individual form elements with #element_validate
- Handling and displaying validation errors
- Practical examples of form validation scenarios
- Best practices for ensuring data integrity and user experience
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.
When your module defines the form and the form controller, you can add your validation logic as part of the form controller. This is done via the implementation of a validateForm() method. The FormBuilder service will automatically invoke this method at the appropriate time during the process of submitting a form. While the validateForm() method is required by \Drupal\Core\Form\FormInterface, an empty method will fulfill that requirement. It's up to you to provide appropriate validation code inside the method.
In this tutorial we'll:
- Use the
validateForm()method of a form controller to verify user input - Demonstrate how to raise errors on a form element when it doesn't pass validation
By the end of this tutorial you should know how to validate your custom forms.
When working with forms that are not created by your code, where you're not implementing the form controller but rather interacting with the form via implementations of hook_form_alter(), you can use the #validate property of the root form element to add additional validation logic in the form of a callback function or method.
In this tutorial we'll:
- Implement a
#validatecallback that raises an error if specific conditions are not met
By the end of this tutorial you should know how to add custom validation logic to any form in Drupal by using a #validate callback.
When defining a new FormElement plugin, or if your constraints are only relevant for a single element, you can use the #element_validate property of an individual element to specify additional validation callbacks.
In this tutorial we'll:
- Add an
#element_validatecallback to a single element in a form to perform validation of just that element.
By the end of this tutorial you should know how to add #element_validate callbacks to any form element in Drupal.
