This manual is no longer being maintained for TYPO3 versions 11.5 and above. The majority of the content has been migrated to the Extbase or Fluid sections in "TYPO3 Explained".
Basic Design Principles¶
None of the design principles here are specific to TYPO3 or Extbase / Fluid. If you are familiar with Object Oriented Programming in PHP, Model-View-Controller, Domain Driven Design and Test-Driven Development, you can safely skip to the next chapter A journey Through the Blog Example.
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 organizations or even in private, others are developed in big teams in the context of major projects. As a newbie writing your first extension, you may struggle with some first-time problems concerning TYPO3, as many big projects are base on homemade Frameworks. So style and architecture of today's extensions are quite heterogeneous. Hence, it is often very difficult to extend or modify existing extensions for your own projects. Before you can do that, you will have to wrap your head around the development style of the respective author or team of authors.
It's one of the goals 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. Using Extbase, small extensions as well as big projects can be implemented in a well-structured way.
Extbase is based on four interconnected and complementary paradigms. You'll encounter 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): The goal of this approach 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 which is 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 as knowledge on these paradigms is easy to find and accessible to everyone.
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 would like to warmly recommend this development technique.
The next chapter explains how the paradigms come together and how the MVC pattern is implemented in Extbase.