Drupal Back End Development

Overview

Enable expert-level Drupal back end development capabilities. Provide comprehensive guidance for custom module development, PHP programming, API usage, hooks, plugins, services, and database operations for Drupal 8, 9, 10, and 11+.

When to Use This Skill

Invoke this skill when working with:

• Custom module development: Creating new Drupal modules
• Hooks: Implementing Drupal hooks to alter system behavior
• Controllers & routing: Building custom pages and routes
• Forms: Creating configuration or custom forms
• Entities: Working with content entities or config entities
• Plugins: Building blocks, field types, formatters, or other plugins
• Services: Creating reusable business logic services
• Database operations: Custom queries and schema definitions
• APIs: Entity API, Form API, Database API, Plugin API

Core Capabilities

1. Custom Module Development

Create complete, standards-compliant Drupal modules:

Quick start workflow:

1. Use module template from assets/module-template/
2. Replace MODULENAME with machine name (lowercase, underscores)
3. Replace MODULELABEL with human-readable name
4. Implement functionality using Drupal APIs
5. Enable module and test: ddev drush en mymodule -y

Module structure:

• .info.yml - Module metadata and dependencies
• .module - Hook implementations
• .routing.yml - Route definitions
• .services.yml - Service definitions
• .permissions.yml - Custom permissions
• src/ - PHP classes (PSR-4 autoloading)
• config/ - Configuration files

Reference documentation:

• references/module_structure.md - Complete module patterns
• references/hooks.md - Hook implementations

2. Hooks System

Implement hooks to alter Drupal behavior:

Common hooks:

• hook_entity_presave() - Modify entities before saving
• hook_entity_insert/update/delete() - React to entity changes
• hook_form_alter() - Modify any form
• hook_node_access() - Control node access
• hook_cron() - Perform periodic tasks
• hook_install/uninstall() - Module installation tasks

Hook pattern:

function MODULENAME_hook_name($param1, &$param2) {
  // Implementation
}

Best practices:

• Implement hooks in .module file only
• Use proper type hints
• Document with PHPDoc blocks
• Check for entity types before processing
• Be mindful of performance

3. Controllers & Routing

Create custom pages and endpoints:

Route definition (.routing.yml):

mymodule.example:
  path: '/example/{param}'
  defaults:
    _controller: '\Drupal\mymodule\Controller\ExampleController::content'
    _title: 'Example Page'
  requirements:
    _permission: 'access content'
    param: \d+

Controller pattern:

namespace Drupal\mymodule\Controller;

use Drupal\Core\Controller\ControllerBase;

class ExampleController extends ControllerBase {
  public function content() {
    return ['#markup' => $this->t('Hello!')];
  }
}

With dependency injection:

public function __construct(EntityTypeManagerInterface $entity_type_manager) {
  $this->entityTypeManager = $entity_type_manager;
}

public static function create(ContainerInterface $container) {
  return new static($container->get('entity_type.manager'));
}

4. Forms API

Build configuration and custom forms:

Configuration form:

class SettingsForm extends ConfigFormBase {
  protected function getEditableConfigNames() {
    return ['mymodule.settings'];
  }

  public function buildForm(array $form, FormStateInterface $form_state) {
    $config = $this->config('mymodule.settings');
    
    $form['api_key'] = [
      '#type' => 'textfield',
      '#title' => $this->t('API Key'),
      '#default_value' => $config->get('api_key'),
    ];
    
    return parent::buildForm($form, $form_state);
  }

  public function submitForm(array &$form, FormStateInterface $form_state) {
    $this->config('mymodule.settings')
      ->set('api_key', $form_state->getValue('api_key'))
      ->save();
    parent::submitForm($form, $form_state);
  }
}

Form validation:

public function validateForm(array &$form, FormStateInterface $form_state) {
  if (strlen($form_state->getValue('field')) < 5) {
    $form_state->setErrorByName('field', $this->t('Too short.'));
  }
}

5. Entity API

Work with content and configuration entities:

Loading entities:

// Load single entity
$node = \Drupal::entityTypeManager()->getStorage('node')->load($nid);

// Load multiple entities
$nodes = \Drupal::entityTypeManager()->getStorage('node')->loadMultiple([1, 2, 3]);

// Load by properties
$nodes = \Drupal::entityTypeManager()->getStorage('node')->loadByProperties([
  'type' => 'article',
  'status' => 1,
]);

Creating/saving entities:

$node = \Drupal::entityTypeManager()->getStorage('node')->create([
  'type' => 'article',
  'title' => 'My Article',
  'body' => ['value' => 'Content', 'format' => 'basic_html'],
]);
$node->save();

Entity queries:

$query = \Drupal::entityQuery('node')
  ->condition('type', 'article')
  ->condition('status', 1)
  ->accessCheck(TRUE)
  ->sort('created', 'DESC')
  ->range(0, 10);
$nids = $query->execute();

6. Plugin System

Create custom plugins (blocks, fields, etc.):

Block plugin:

/**
 * @Block(
 *   id = "mymodule_custom_block",
 *   admin_label = @Translation("Custom Block"),
 * )
 */
class CustomBlock extends BlockBase {
  public function build() {
    return ['#markup' => 'Block content'];
  }
  
  public function blockForm($form, FormStateInterface $form_state) {
    $form['setting'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Setting'),
      '#default_value' => $this->configuration['setting'] ?? '',
    ];
    return $form;
  }
  
  public function blockSubmit($form, FormStateInterface $form_state) {
    $this->configuration['setting'] = $form_state->getValue('setting');
  }
}

7. Services & Dependency Injection

Create reusable services:

Service definition (.services.yml):

services:
  mymodule.custom_service:
    class: Drupal\mymodule\Service\CustomService
    arguments: ['@entity_type.manager', '@current_user']

Service class:

namespace Drupal\mymodule\Service;

class CustomService {
  protected $entityTypeManager;
  protected $currentUser;

  public function __construct(EntityTypeManagerInterface $entity_type_manager, AccountProxyInterface $current_user) {
    $this->entityTypeManager = $entity_type_manager;
    $this->currentUser = $current_user;
  }

  public function doSomething() {
    // Business logic
  }
}

8. Database Operations

Execute custom queries:

Using Database API:

$database = \Drupal::database();

// Select query
$query = $database->select('node_field_data', 'n')
  ->fields('n', ['nid', 'title'])
  ->condition('type', 'article')
  ->condition('status', 1)
  ->range(0, 10);
$results = $query->execute()->fetchAll();

// Insert
$database->insert('mymodule_table')
  ->fields(['name' => 'Example', 'value' => 123])
  ->execute();

// Update
$database->update('mymodule_table')
  ->fields(['value' => 456])
  ->condition('name', 'Example')
  ->execute();

Schema definition (.install file):

function mymodule_schema() {
  $schema['mymodule_table'] = [
    'fields' => [
      'id' => ['type' => 'serial', 'not null' => TRUE],
      'name' => ['type' => 'varchar', 'length' => 255, 'not null' => TRUE],
      'value' => ['type' => 'int', 'not null' => TRUE, 'default' => 0],
    ],
    'primary key' => ['id'],
    'indexes' => ['name' => ['name']],
  ];
  return $schema;
}

Development Workflow

Creating a Custom Module

1. Scaffold the module:

   cp -r assets/module-template/ /path/to/drupal/modules/custom/mymodule/
   cd /path/to/drupal/modules/custom/mymodule/
   mv MODULENAME.info.yml mymodule.info.yml
   mv MODULENAME.module mymodule.module
   mv MODULENAME.routing.yml mymodule.routing.yml

2. Update module files:

   • Replace MODULENAME with machine name
   • Replace MODULELABEL with readable name
   • Update .info.yml dependencies
   • Customize controller, routes, logic

3. Enable and test:

   ddev drush en mymodule -y
   ddev drush cr

4. Develop iteratively:

   • Implement functionality
   • Clear cache: ddev drush cr
   • Test thoroughly
   • Check logs: ddev drush watchdog:tail

Standard Development Workflow

1. Plan: Identify what APIs/hooks you need
2. Code: Implement using Drupal APIs
3. Test: Enable module, clear cache, test functionality
4. Debug: Check logs, use Xdebug if needed
5. Refine: Optimize, add tests, improve code quality

Best Practices

Module Development

1. PSR-4 autoloading: Follow namespace conventions
2. Dependency injection: Use DI in classes
3. Hooks: Implement only in .module files
4. Type hints: Use proper PHP type declarations
5. Documentation: Add PHPDoc blocks
6. Testing: Write automated tests

Code Quality

1. Drupal coding standards: Follow PHPCS rules
2. Security: Validate input, sanitize output, check permissions
3. Performance: Cache when possible, optimize queries
4. Accessibility: Ensure forms and pages are accessible
5. Internationalization: Use $this->t() for all strings

API Usage

1. Entity API: Prefer entity operations over direct DB queries
2. Configuration: Use Config API for settings
3. State API: Use for temporary/non-exportable data
4. Cache API: Implement caching for expensive operations
5. Queue API: Use for long-running tasks

Common Patterns

Event Subscriber

class MyModuleSubscriber implements EventSubscriberInterface {
  public static function getSubscribedEvents() {
    return [KernelEvents::REQUEST => ['onRequest', 0]];
  }

  public function onRequest(RequestEvent $event) {
    // Handle event
  }
}

Custom Permission

# mymodule.permissions.yml
administer mymodule:
  title: 'Administer My Module'
  restrict access: true

Custom Access Check

class CustomAccessCheck implements AccessInterface {
  public function access(AccountInterface $account) {
    return AccessResult::allowedIf($account->hasPermission('access content'));
  }
}

Troubleshooting

Module Not Appearing

• Check .info.yml syntax
• Verify core_version_requirement
• Clear cache: ddev drush cr

Hooks Not Working

• Verify hook name is correct
• Clear cache after adding hooks
• Check module weight if hook order matters

Class Not Found

• Verify PSR-4 namespace matches directory
• Clear cache to rebuild class registry
• Check autoloading with composer dump-autoload

Database Errors

• Check schema definition syntax
• Run ddev drush updb after schema changes
• Verify table/column names in queries

Resources

Reference Documentation

• references/hooks.md - Common hooks with examples

  • Entity hooks
  • Form hooks
  • Node hooks
  • Installation hooks
  • Token hooks

• references/module_structure.md - Module patterns

  • Controllers and routing
  • Forms (config and custom)
  • Plugins (blocks, fields, etc.)
  • Services and DI
  • Event subscribers

Asset Templates

• assets/module-template/ - Module scaffold
  • .info.yml metadata
  • .module hook file
  • .routing.yml routes
  • Example controller

Version Compatibility

Drupal 8 vs 9 vs 10 vs 11

• Core APIs: Largely consistent across versions
• PHP requirements: 8.x (7.0+), 9.x (7.3+), 10.x (8.1+), 11.x (8.3+)
• Deprecations: Check change records when upgrading
• Symfony: Different Symfony versions in each Drupal version

See Also

• drupal-frontend - Theme development, Twig templates
• drupal-tooling - DDEV and Drush development tools
• Drupal API - Official API documentation