.. include:: /Includes.rst.txt .. _cgl-services: Services ^^^^^^^^ Characteristica """"""""""""""" * Services MUST be used as objects, they are never static * A single service MUST consist of one class only * Services MUST be located in a :code:`Service/` directory and MUST end with :code:`Service`, eg. :code:`Service/FoobarService.php` * Service instances MAY hold state, but SHOULD be stateless * Services MAY use configuration, but SHOULD not * Services MAY have multiple entry points, but SHOULD have only one * Services SHOULD NOT be singletons Rationale """"""""" A “service” in this context is meant as the relatively short-sighted process of putting a class into a :code:`Service/` subfolder and calling it a :code:`WhateverService`. It does not have too much to do with the DDD Service context, which is broader. This section is just about which scope can be expected for classes residing in a Service folder within core extensions. From this point of view, services in TYPO3 world are a relatively slim class construct that encapsulates a specific concern. It is too big for a small static method, it may hold state, but it is still just a relatively small scope. Each service consists typically of only a single class. A bigger construct with interfaces, multiple sub classes is not called a service anymore. The above MAY and SHOULD mean that a single service MAY do a single one or two of them, but if for instance a service is relatively big, has many entry points, keeps state and depends on configuration, this is too much and is a sign it should be modeled in a different and more dedicated and more disjoint way. The main risk with service classes is that they pile up to a conglomeration of helper stuff classes that are hanging around without good motivation. It is important that a service class should not be a bin for something that just does not fit to a different better place within the scope of a specific extension. Good examples """"""""""""" * :code:`\TYPO3\CMS\Extbase\Service\CacheService` * Small and straight scope with useful helpers * It is a singleton, but that is feasible in this case Bad examples """""""""""" * :code:`\TYPO3\CMS\Core\Service\AbstractService`, :code:`TYPO3\CMS\Sv\AuthenticationService` * Not modeled in a sane way, this should be within :code:`Core/Authentication` * Far too complex, class abstraction and extending classes Further reading """"""""""""""" See http://gorodinski.com/blog/2012/04/14/services-in-domain-driven-design-ddd/.