Using hook_entity_form_alter() for entity formsfor Drupal 8 , 9 , 10 , and 11

In the world of Drupal, hooks are a powerful way to interact and modify the behavior of core functionalities. hook_entity_form_alter() offers developers a dynamic toolset for customizing entity forms without altering the original entity form definitions. This approach allows for flexible adaptation to specific user needs and system requirements.

Understanding hook_entity_form_alter()

The hook_entity_form_alter() function is part of Drupal's extensive hook system. It allows developers to alter the form array before it is rendered, offering the flexibility to adjust form attributes, add new fields, or redefine user interface elements based on specific conditions.

Applications of hook_entity_form_alter()

• Dynamic Field Modification: Change widget types or properties based on contextual needs.
• Conditional Visibility: Show or hide fields depending on user roles or other criteria.
• Validation and Logic: Introduce additional validation, default values, or preprocessing logic directly in the form structure.

Implementing hook_entity_form_alter()

Continuing our Fruit example, we will demonstrate how to use hook_entity_form_alter() to dynamically customize the fruit form by adding a field that prompts an optional note when the fruit color is set to 'Red'.

Step 1: Define the Hook

To use hook_entity_form_alter(), implement it in your custom module's .module file. The hook is invoked each time an entity form is built:

// In fruit_module.module
use Drupal\Core\Form\FormStateInterface;

/**
 * Implements hook_entity_form_alter().
 */
function fruit_module_entity_form_alter(array &$form, FormStateInterface $form_state, $form_id) {
  if ($form_id == 'fruit_edit_form' || $form_id == 'fruit_add_form') {
    // Add a 'note' field conditionally based on the color.
    $form['note'] = [
      '#type' => 'textarea',
      '#title' => t('Note'),
      '#description' => t('Add any additional notes about the fruit.'),
      '#states' => [
        'visible' => [
          ':input[name="color"]' => ['value' => 'Red'],
        ],
      ],
    ];

    // Alter the form submit handler if needed.
    $form['#submit'][] = 'fruit_module_custom_submit';
  }
}

Step 2: Implement Custom Submit Logic

You might want to include custom functionality upon form submission. Add a custom submit handler within the same file:

/**
 * Custom submit handler for the fruit form.
 */
function fruit_module_custom_submit(array &$form, FormStateInterface $form_state) {
  // Here you might save additional form values or log data.
  $note = $form_state->getValue('note');
  drupal_set_message(t('Your note has been saved: @note', ['@note' => $note]));
}

Step 3: Test and Review

After implementing your hook, test the form functionality in your Drupal site. Confirm the "Note" field appears when the fruit color is set to "Red" and that the rest of the form behaves as expected.

Considerations for Using hook_entity_form_alter()

• Keep the logic lightweight to not hamper performance by unnecessarily altering unrelated forms.
• Test thoroughly, especially when conditions are based on user input or role-specific permissions.
• Use descriptive comments to clarify the logic and rationale behind alterations for future maintenance.

Summary

Using hook_entity_form_alter() provides you with the flexibility and power to adapt Drupal forms dynamically, creating a more customized experience for your site's users. Whether you need to add or hide fields, change form behavior, or introduce additional business logic, this hook is a valuable tool in any Drupal developer's toolkit.

Teaser for the Next Lesson

In the next lesson, we will explore conditionally creating form alterations using contexts such as user roles and permissions to tailor the user experience even further. Stay tuned for more insights into Drupal's flexible and powerful customization capabilities!