Basic Principles

TYPO3 comes with an impressive variety of available extensions. As usual with Open Source Projects, these extensions have been written by various Programmers. Extensions are used in all sorts of projects: Some are written for use in small clubs or even in private, others are developed in big teams in the context of major projects. While a newbie, writing his first extension, may hassle with some first-time problems concerning TYPO3, many big projects are based on homemade Frameworks. So style and architecture of today’s extensions are quite inhomogeneous. Hence it is often very difficult to extend or modify existing Extensions for own projects: Before being able to do so, you have to intensively dig into the way of thinking and programming of the respective author or team of authors.

It’s one of the aims of Extbase to reduce this inconsistency in extensions. Approved paradigms of programming lead to fast success for newbies and protect Developers from having to deal with complex database queries or potential security holes like SQL-Injections or XSS-Attacks. Based on Extbase small Extensions as well as big projects can be realized in a well-structured way.

Extbase is based on four interconnected and complementary paradigms, which we like to present in this chapter. You’ll find these during the whole project cycle, from planning to realization and maintenance of your extension:

• Object-Oriented Programming (OOP): describes how to encapsulate associated real world aspects to abstract objects in a software
• Domain-Driven Design (DDD): Goal of this Approach of developing is to transcribe terms, rules and actions of the problem at hand in an adequate way.
• Model-View-Controller (MVC): This programming paradigm leads to a clear isolation of data, control of actions and logic of interaction.
• Test-Driven Development (TDD): This approach is a basic technique for generating code being stable, resilient to errors and legible - and therefore maintainable.

Each of these four paradigms are well known in professional software development and more or less widespread. This results in a big advantage when using Extbase. Until now an expert in developing TYPO3 extensions was mainly an expert in usage (and by-passing) of the application programming interface (API) of TYPO3. Extbase in contrast will demand additional knowledge and skills in domains that are useful and effective far beyond the TYPO3 Community. Thus you can access an extensive accumulation of experience in form of books, forums or personal contacts – an important aspect of the future of TYPO3.

Knowledge in Object-Oriented Programming, Domain-Driven Design and the MVC-paradigm is essential for working with extbase. Knowledge of Test-Driven Development is not absolutely necessary for understanding nor using extbase. Nevertheless we like to warmly recommend this technique of developing.

• Object-oriented programming in PHP
  • Why Object Orientation after all?
  • Classes and Objects
  • The arrow operator
  • $this
  • Constructor
  • Inheritance of Classes
  • Overriding Properties and Methods
  • Access to the parent class through “parent”
  • Abstact classes
  • Interfaces
  • Visibilities: public, private and protected
  • Access to Properties
  • Access to Methods
  • Static Methods and Properties
  • Important design- and architectural patterns
  • Singleton
  • Prototype
• Domain-Driven Design
  • Develop a common language
  • To model the domain
  • Reconstitute objects with repositories
• Model-View-Controller in Extbase
  • The Interaction of Model, View and Controller
• Test-Driven Development
  • First test, then implementing
  • Example
  • Test individual objects
  • Dependency Injection
  • Mock-Objects
• Conclusion