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 MUST end withService
, eg.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 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, 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¶
\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\AbstractService
,- Not modeled in a sane way, this should be within
Core/Authentication
- Far too complex, class abstraction and extending classes
- Not modeled in a sane way, this should be within
Further Reading¶
See http://gorodinski.com/blog/2012/04/14/services-in-domain-driven-design-ddd/.