Design Patterns in Drupal 7

My talk on Software Engineering Design Patterns implemented in Drupal at Drupal Camp Singapore 2013.

Transcript

1. Design Patterns in Drupal 7 April 2013 Drupal Camp Singapore
2. Housekeeping Slides http://bit.ly/drupalcampsg-ddp I'm awesome.* - It's a debatable claim
3. Hello, there! Amarnath Ravikumar Teamie Engineer, NUS Grad Drupal enthusiast & contributor. http://twitter.com/amarnus
4. Motivation (1)
5. Motivation (2) An added benefit comes when the framework is documented with the design patterns it uses. People who know the patterns gain insight into the framework faster. Even people who don't know the patterns can benefit from the structure they lend to the framework's documentation. - Gang of Four, Elements of Reusable Object-oriented Software.
6. Behind Captain Drupal...
7. ... sits an elegant web framework.
8. Design Patterns could be.. Drupal-specific, re-usable ideas • Using drupal_static() • http://dropbucket.org/node/254 • Use confirm_form() on entity delete OR Generic, abstract ideas implemented in Drupal. A fresh look at things you already know & love.
9. Design Patterns are.. Named ideas Focus on code-reuse & maintainability. Implementation-independent Free to discuss & compare implementations ◦ Cross-framework ice breaker? :) A way to evaluate a framework* Potential framework entry-point
10. Design Patterns in Drupal.. Subtle, implicit • OOP misconception • Documentation Why should you know? • Architecting complex, custom modules • For kicks?
11. Basic Ideas Loose coupling of components ◦ Scale. Models real world. Inversion of control Code Reuse / DRY Indirection • theme_button() v theme("button")
12. Factory, Strategy patterns (1) Factory: Object builder Strategy: A particular solution to achieve a task. Eg. Mail system Cache backend Database connection
13. Factory, Strategy patterns (2) Eg. (contd) MailSystemInterface DefaultMailSystem (core) DevelMailLog (devel) AmazonSESMailSystem (amazon_ses) DrupalCacheInterface DrupalDatabaseCache Redis_Cache
14. Factory, Strategy patterns (3) Non-OOP can? Drupal's swappable session backend. Source code file (Object) Drupal core (Factory) Access modifiers (by Convention) Interface (by Convention)
15. Observer, Mediator patterns (1) React to events in another component (subject) Listener/Handler/Callback/Subscriber In Drupal, we have: • Event Hooks Eg. hook_entity_(presave|insert|update|delete) • Triggers & Actions
16. Observer, Mediator patterns (2) Subscription (Expressing intent) Typically, there is coupling between the observers and the subject but not between themselves. Drupal: Subject - Mediator* - Observers
17. Observer, Mediator patterns (3) A protocol to govern the order in which observers will be notified independent of the subject. The protocol for an observer to express intent can vary independent of the subject. Can account for dependencies between observers (if there are)
18. Observer, Mediator patterns (4) Classical jQuery Symfony Drupal
19. Dependency Injection Components declare dependencies. Dependency resolution offloaded to the framework. Eg. hook_menu() (Core), hook_services_resources() (Services)
20. Chain of Responsibility (1) Delegate the responsibility of handling a request to a set of candidates instead of one, allowing fallback. Exception handling* Eg. Hook suggestions in the Drupal theme system.
21. Chain of Responsibility (2) At http://example.com/foo/bar theme('page', $variables) page--foo.tpl.php page--foo--%.tpl.php page--foo--bar.tpl.php page--logged_out.tpl.php page.tpl.php
22. Decorator Adds additional behaviors/properties (enhancements) to an object at run-time. Drupal's QueryExtendableInterface Entity API's metadata wrapper object*
23. Adapter Same as strategy but top-down instead of bottom-up.* Eg. Database Drivers. MySQL SQLLite MongoDB
24. More Anti-patterns PAC (Architectural pattern) Other contrib: ctools, views Other patterns that hooks manifest. Drupal 8
25. Review 1. Basic Ideas 2. Design Patterns ◦ Factory, Strategy ▪ Object-oriented Design ◦ Observer, Mediator ◦ Dependency Injection ◦ Chain of Responsibility ◦ Decorator ◦ Adapter
27. Q & A / Debate?