Code Reference Map

When to Use

Need to find core code examples demonstrating each SOLID principle.

Core Examples by Principle

Single Responsibility Principle

• /core/modules/node/src/NodeGrantDatabaseStorage.php -- Focused on access grants only
• /core/modules/node/src/Hook/NodeEntityHooks.php -- Entity hooks separated from form hooks
• /core/modules/node/src/Hook/NodeFormHooks.php -- Form hooks separated from entity hooks
• /core/lib/Drupal/Core/Form/FormBase.php -- Form structure only, delegates to services

Open/Closed Principle

• /core/lib/Drupal/Core/Plugin/PluginBase.php -- Plugin system foundation, open for extension
• /core/lib/Drupal/Core/Block/BlockBase.php -- Block plugins extend without modifying core
• /core/modules/node/src/Hook/NodeEntityHooks.php -- Using hooks to extend behavior
• /core/lib/Drupal/Core/Routing/RouteSubscriberBase.php -- Event subscriber pattern

Liskov Substitution Principle

• /core/lib/Drupal/Core/Entity/ContentEntityBase.php -- Base contract all content entities honor
• /core/modules/node/src/Entity/Node.php -- Extends ContentEntityBase, honors contract
• /core/lib/Drupal/Core/Form/ConfigFormBase.php -- Extends FormBase, adds config behavior
• /core/lib/Drupal/Core/Access/AccessResult.php -- Immutable value objects, substitutable

Interface Segregation Principle

• /core/lib/Drupal/Core/Entity/EntityInterface.php -- Minimal base interface
• /core/lib/Drupal/Core/Entity/EntityOwnerInterface.php -- Focused on ownership only
• /core/lib/Drupal/Core/Entity/EntityPublishedInterface.php -- Focused on published status only
• /core/lib/Drupal/Core/DependencyInjection/ContainerInjectionInterface.php -- Single method interface
• /core/lib/Drupal/user/EntityOwnerTrait.php -- Trait implementing focused interface

Dependency Inversion Principle

• /core/core.services.yml -- Service definitions, interface-based dependencies
• /core/modules/node/node.services.yml -- Autowiring, service aliases
• /core/lib/Drupal/Core/Form/FormBase.php -- ContainerInjectionInterface for DI
• /core/lib/Drupal/Core/DependencyInjection/AutowireTrait.php -- Automatic dependency resolution

Additional Architecture Examples

• /core/lib/Drupal/Core/Entity/EntityStorageInterface.php -- Interface for entity storage
• /core/lib/Drupal/Core/Config/ConfigFactoryInterface.php -- Interface for config access
• /core/lib/Drupal/Core/Database/Connection.php -- Database abstraction
• /core/lib/Drupal/Core/Plugin/DefaultPluginManager.php -- Plugin discovery and instantiation

See Also

• Reference: All files in /core/lib/Drupal/Core/
• Reference: Entity examples in /core/modules/node/src/Entity/
• Reference: Plugin examples in /core/lib/Drupal/Core/Plugin/