Adding entity-specific validation logicfor Drupal 8 , 9 , 10 , and 11

Continuing on our journey through Drupal's Form API, it’s time to focus on adding validation logic customized specifically for your entities. Validation is crucial for maintaining data accuracy and integrity, ensuring that only well-formed and expected data is persisted in the system.

Why Entity-Specific Validation?

When working with Drupal entities, there are often unique constraints and business rules that need enforcement beyond basic form validation such as non-empty fields or numeric values. Custom validation logic allows you to implement these specific rules, contributing to robust system architecture and better user experience.

Benefits of Entity-Specific Validation

• Data Integrity: Prevents the storage of invalid data and ensures data quality.
• User Feedback: Provides real-time feedback, guiding users toward correct data entry.
• Business Rules Enforcement: Implements custom constraints that reflect business logic.

Implementing Validation in Entity Forms

In the previous lesson, we extended the form for the Fruit entity. Let’s continue by adding entity-specific validation logic. For example, we'll ensure that a fruit's name is unique and the color is not a number.

Step 1: Defining Validation Rules

Define your validation rules in the custom form class by implementing the validateForm() method:

// In src/Form/FruitEditForm.php
namespace Drupal\fruit_module\Form;

use Drupal\Core\Form\FormStateInterface;

/**
 * Form controller for the Fruit entity edit forms.
 */
class FruitEditForm extends FruitForm {

  public function validateForm(array &$form, FormStateInterface $form_state) {
    parent::validateForm($form, $form_state);

    // Retrieve the current values.
    $name = $form_state->getValue('name');
    $color = $form_state->getValue('color');

    // Ensure name uniqueness.
    $database = \Drupal::database();
    $existing = $database->select('fruit', 'f')
      ->fields('f', ['name'])
      ->condition('name', $name)
      ->execute()
      ->fetchField();

    if ($existing && $this->entity->isNew()) {
      $form_state->setErrorByName('name', $this->t('The fruit name %name already exists.', ['%name' => $name]));
    }

    // Color should not contain only numbers.
    if (is_numeric($color)) {
      $form_state->setErrorByName('color', $this->t('The color field should not be a number.'));
    }
  }
}

Step 2: Implement User-Friendly Feedback

Provide clear and concise validation messages that help users understand the problem and how to correct it. Consider the following principles:

• Be specific about the error.
• Indicate the correction needed.
• Use simple, non-technical language.

The code snippet above checks if the name already exists in the fruit table and ensures that the color field does not consist solely of numeric characters. If these validations fail, users receive descriptive error messages.

Step 3: Testing and Refining

After implementing validation logic, thoroughly test your form to ensure that rules work as intended across all use cases. Validate with different combinations of inputs to ensure robust error handling and user feedback.

Summary

Incorporating entity-specific validation logic in Drupal forms is essential for protecting the integrity of your data and providing a smooth, informative user experience. By implementing custom checks and providing clear feedback, you ensure that only valid data is saved, aligning with system requirements and user expectations.

Teaser for the Next Lesson

Our next lesson will cover saving entities using the submitForm() method. We'll explore best practices for efficiently persisting data and managing submission workflows in Drupal. Stay tuned to master these advanced techniques!