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 Service/ directory and the class and file name MUST end with Service, eg. Service/FoobarService.php.

  • Service instances MAY hold a state, but they SHOULD be stateless.

  • Services MAY use their own configuration, but they SHOULD not.

  • Services MAY have multiple entry points, but they 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 Service/ subfolder and calling it a 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, a service in the TYPO3 world is a relatively slim class construct that encapsulates a specific concern. It is too big for a small static method, it may hold a 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 characteristica MAY and SHOULD mean that a single service MAY do a single one or two of them, but if for instance a service would become relatively big, if it would have many entry points, if it would keep states and depend on configuration, this would be too much. This would be a sign that 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

  • \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

  • \TYPO3\CMS\Core\Service\AbstractAuthenticationService,

    • Not modeled in a sane way, this should be within Core/Authentication

    • Far too complex, class abstraction and extending classes