Dependency injection¶
New in version 10.0: Feature: #84112 - Symfony dependency injection for core and extbase
Note
Deprecated since version 11.4: Deprecation: #94619 - Extbase ObjectManager
The class \TYPO3\CMS\Extbase\Object\ObjectManager
has been deprecated
with TYPO3 v11.4. Classes should be updated to avoid both,
\TYPO3\CMS\Extbase\Object\ObjectManager
and
\TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance()
whenever
possible for resolving service dependencies.
This page
Abstract¶
This chapter explains "Dependency Injection (DI)" as used in TYPO3. Readers interested in the general concepts and principles may want to look at, for example, Dependency Injection in "PHP The Right Way" or What is dependency injection? by Fabien Potencier. Whenever a class has a service dependency to another class the technique of dependency injection should be used to satisfy that need. TYPO3 uses a Symfony component for dependency injection. The component is PSR-11 compliant, and it is used throughout Core and extensions to standardize object initialization. By default all API services shipped with the TYPO3 Core system extensions offer dependency injection. The recommended usage is constructor injection. Available as well are method injection and interface injection. To activate the Symfony component for dependency injection a few lines of configuration are necessary.
Introduction¶
The title of this chapter is "dependency injection" (DI), but the scope is a bit broader: In general, this chapter is about TYPO3 object lifecycle management and how to obtain objects, with one sub-part of it being dependency injection.
The underlying interfaces are based on the PHP-FIG (PHP Framework Interop Group) standard PSR-11 Container interface, and the implementation is based on Symfony service container and Symfony dependency injection components, plus some TYPO3 specific sugar.
This chapter not only talks about Symfony DI and its configuration via Services.yaml
,
but also a bit about services in general, about GeneralUtility::makeInstance()
and the
SingletonInterface
. And since the TYPO3 core already had an object lifecycle management
solution with the extbase ObjectManager
before Symfony services were implemented, we'll
also talk about how to transition away from it towards the core-wide Symfony solution.
Background and history¶
Obtaining object instances in TYPO3 has always been straightforward: Call
GeneralUtility::makeInstance(\MyVendor\MyExtension\Some\Class::class)
and hand over
mandatory and optional __construct()
arguments as additional arguments.
There are two quirks to that:
First, a class instantiated through makeInstance() can implement
SingletonInterface
. This empty interface definition tells makeInstance() to instantiate the object exactly once for this request, and if another makeInstance() call asks for it, the same object instance is returned - otherwise makeInstance() always creates a new object instance and returns it.Second,
makeInstance()
allows "XCLASSing". This is a - rather dirty - way to substitute a class with a custom implementation. XCLASS'ing in general is brittle and seen as a last resort hack if no better solution is available. In connection with Symfony containers, XCLASSing services should be avoided in general and service overrides should be used instead. Replacing the XCLASS functionality in TYPO3 is still work in progress. In contrast, XCLASSing is still useful for data objects, and there is no good other solution yet.
Using makeInstance()
worked very well for a long time. It however lacked a feature
that has been added to the PHP world after makeInstance()
had been invented: Dependency injection.
There are lots of articles about dependency injection on the net, so we won't go too deep
here but rather explain the main idea: The general issue appears when classes follow the
separation of concerns
principle.
One of the standard examples is logging. Let's say a class's responsibility is the creation of users - it checks everything and finally writes a row to database. Now, since this is an important operation, the class wants to log an information like "I just created user 'foo'". And this is where dependency injection enters the game: Logging is a huge topic, there are various levels of error, information can be written to various destinations and so on. The little class does not want to deal with all those details, but just wants to tell the framework: "Please give me some logger I can use and that takes care of all details, I don't want to know about details". This separation is the heart of single responsibility and separation of concerns.
Dependency injection does two things for us here: First, it allows separating concerns, and second, it hands the task of finding an appropriate implementation of a dependency over to the framework, so the framework decides - based on configuration - which specific instance is given to the consumer. Note in our example, the logging instance itself may have dependencies again - the process of object creation and preparation may be further nested.
In more abstract software engineering terms: Dependency injection is a pattern used to delegate the task of resolving class dependencies away from a consumer towards the underlying framework.
Back to history: After makeInstance()
has been around for quite a while and lacked an
implementation of dependency injection, Extbase appeared in 2009. Extbase brought a first container
and dependency injection solution, it's main interface being the Extbase ObjectManager
.
The Extbase object manager has been widely used for a long time, but suffered from some
issues younger approaches don't face. One of the main drawbacks of Extbase object manager
is the fact that it's based on runtime reflection: Whenever an object is to be instantiated,
the object manager scans the class for needed injections and prepares dependencies to be
injected. This process is quite slow though mitigated by various caches. And these also
come with costs. In the end, these issues have been the main reason the object manager
was never established as a main core concept but only lived in Extbase scope.
The object lifecycle and dependency injection solution based on Symfony DI has been
added in TYPO3v10 and is a general core concept: Next to the native
dependency injection, it is also wired into makeInstance()
as a long living
backwards compatibility solution, and it fully substitutes the Extbase object manager. In
contrast to the Extbase solution, Symfony based object management does not have the
overhead of
expensive runtime calculations. Instead it is an instance wide build-time solution: When
TYPO3 bootstraps, all object creation details of all classes are read from
a single cache file just once, and afterwards no expensive calculation is required
for actual creation.
Symfony based DI was implemented in TYPO3 v10 and usage of the Extbase ObjectManager was discouraged. With TYPO3 v11 the core doesn't use the ObjectManager any more. It is actively deprecated in v11 and thus leads to 'deprecation' level log entries.
With TYPO3 v12 the Extbase ObjectManager is actually gone. Making use of
Symfony DI integration still continues. There
are still various places in the core to be improved. Further streamlining will
be done over time. For instance, the final fate of makeInstance()
and the SingletonInterface
has not fully been decided on yet. Various
tasks remain to be solved in younger TYPO3 developments to further improve the
object lifecycle management provided by the core.
Build-time caches¶
To get a basic understanding of the core's lifecycle management it is helpful to get a rough insight on the main construct. As already mentioned, object lifecycle management is conceptualized as steps to take place at build-time. It is done very early and only once during the TYPO3 bootstrap process. All calculated information is written to a special cache that can not be reconfigured and is available early. On subsequent requests the cache file is loaded. Extensions can not mess with the construct if they adhere to the core API.
Besides being created early, the state of the container is independent and exactly the same in frontend, backend and CLI scope. The same container instance may even be used for multiple requests. This is becoming more and more important nowadays with the core being able to execute sub requests. The only exception to this is the Install Tool: It uses a more basic container that "cannot fail". This difference is not important for extension developers however since they can't hook into the Install Tool at those places anyways.
The Symfony container implementation is usually configured to actively scan the
extension classes for needed injections. All it takes are just a couple
of lines within the Services.yaml
file. This should be done within all extensions that
contain PHP classes and it is the fundamental setup we will outline in the following sections.
For developers, it is important to understand that dealing with Symfony DI is an early core bootstrap thing. The system will fail upon misconfiguration, so frontend and backend may be unreachable.
Attention
Errors in the DI cache may block frontend and backend!
The DI cache does not heal by itself but needs to be cleared manually!
The container cache entry (at the time of this writing) is not deleted when a
backend admin user clicks "Clear all cache" in the backend top toolbar. The only
way to force a DI recalculation is using the "Admin tools" -> "Maintenance" -> "Flush Caches"
button of the backend embedded Install Tool or the standalone Install Tool (/typo3/install.php
) itself. This
means: Whenever core or an extension fiddles with DI (or more general "Container") configuration,
this cache has to be manually emptied for a running instance by clicking this button.
The backend Extension Manager however does empty the cache automatically when loading or unloading extensions.
Another way to quickly drop this cache during development is to remove all
var/cache/code/di/*
files, which reside in typo3temp/
in Legacy Mode
instances or elsewhere in Composer Mode instances (see Environment). TYPO3 will
then recalculate the cache upon the next access, no matter if it's a frontend, a backend
or a CLI request.
The main takeaway is: When a developer fiddles with container configuration,
the cache needs to be manually cleared. And if some configuration issue slipped in,
which made the container or DI calculation fail, the system does not heal itself and
needs both a fix of the configuration plus probably a cache removal. The standalone Install
Tool however should always work, even if the backend breaks down, so the "Flush caches"
button is always reachable. Note that if the container calculation fails, the
var/log/typo3_*
files contain the exception with backtrace!
Important terms¶
We will continue to use a couple of technical terms in this chapter, so let's quickly define them to align. Some of them are not precisely used in our world, for instance some Java devs may stumble upon "our" understanding of a prototype.
- Prototype
The broad understanding of a prototype within the TYPO3 community is that it's simply an object that is created anew every time. Basically the direct opposite of a singleton. In fact, the prototype pattern describes a base object that is created once, so
__construct()
is called to set it up, after that it is cloned each time one wants to have a new instance of it. The community isn't well aware of that, and the core provides no "correct" prototype API, so the word prototype is often misused for an object that is always created anew when the framework is asked to create one.- Singleton
A singleton is an object that is instantiated exactly once within one request. If an instance is requested and the object has been created once already, the same instance is returned. Codewise, this is sometimes done by implementing a static
getInstance()
method that parks the instance in a property. In TYPO3, this can also be achieved by implementing theSingletonInterface
, wheremakeInstance()
then stores the object internally. Within containers, this can be done by declaring the object as shared (shared: true
), which is the default. We'll come back to details later. Singletons must not have state - they must act the same way each time they're used, no matter where, how often or when they've been used before. Otherwise the behavior of a singleton object is undefined and will lead to obscure errors.- Service
This is another "not by the book" definition. We use the understanding "What is a service?" from Symfony: In Symfony, everything that is instantiated through the service container (both directly via
$container->get()
and indirectly via DI) is a service. These are many things - for instance controllers are services, as well as - non static - utilities, repositories and obvious classes like mailers and similar. To emphasize: Not only classes named with a*Service
suffix are services but basically anything. It does not matter much if those services are stateless or not. Controllers, for instance, are usually not stateless. (This is just a configuration detail from this point of view.) Note: The TYPO3 Core does not strictly follow this behavior in all cases yet, but it strives to get this more clean over time.- Data object
Data objects are the opposite of services. They are not available through service containers. Here calling
$container->has()
returnsfalse
and they can not be injected. They are instantiated either withnew()
orGeneralUtility::makeInstance()
. Domain models or DTO are a typical example of data objects.Note: Data objects are not "service container aware" and do not support DI. Although the TYPO3 core does not strictly follow this rule in all cases until now the ambition is to get this done over time.
Using DI¶
Now that we have a general understanding of what a service and what a data object is, let's turn to usages of services. We will mostly use examples for this.
The general rule is: Whenever your class has a service dependency to another class, one of the following solutions should be used.
When to use Dependency Injection in TYPO3¶
Class dependencies to services should be injected via constructor injection or
setter methods. Where possible, Symfony dependency injection should be used for
all cases where DI is required.
Non-service "data objects" like Extbase domain model instances or DTOs should
be instantiated via \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance()
if they are non-final and support XCLASSing. For final classes without
dependencies plain instantiation via the new
keyword must be used.
In some APIs dependency injection cannot be used yet. This applies to classes that need specific data in their constructors or classes that are serialized and deserialized as, for example, scheduler tasks.
When dependency injection cannot be used directly yet, create a service class and make it public
in the Configuration/Services.yaml
. Create an instance of the service class via
GeneralUtility::makeInstance(...)
you can then use dependency injection in the service class.
Constructor injection¶
Assume we're writing a controller that renders a list of users. Those users are
found using a custom UserRepository
, so the repository service is a direct dependency of the
controller service. A typical constructor dependency injection to resolve the
dependency by the framework looks like this:
namespace MyVendor\MyExtension\Controller;
use MyVendor\MyExtension\Repository\UserRepository;
final class UserController
{
private UserRepository $userRepository;
public function __construct(UserRepository $userRepository)
{
$this->userRepository = $userRepository;
}
}
Here the Symfony container sees a dependency to UserRepository
when scanning __construct()
of the UserController
. Since autowiring is enabled by default (more on that below), an instance of the
UserRepository
is created and provided when the controller is created.
Method injection¶
A second way to get services injected is by using inject*()
methods:
namespace MyVendor\MyExtension\Controller;
use MyVendor\MyExtension\Repository\UserRepository;
final class UserController
{
private ?UserRepository $userRepository = null;
public function injectUserRepository(UserRepository $userRepository)
{
$this->userRepository = $userRepository;
}
}
This ends up with the basically the same result as above: The controller instance has
an object of type UserRepository
in class property $userRepository
.
The injection via methods was introduced by Extbase and TYPO3 core implemented it in addition to
the default Symfony constructor injection. Why did we do that, you may ask? Both
strategies have subtle differences: First, when using inject*()
methods, the type
hinted class property needs to be nullable, otherwise PHP >= 7.4 throws a warning
since the instance is not set during __construct()
. But that's just an
implementation detail. More important is an abstraction scenario. Consider this case:
namespace MyVendor\MyExtension\Controller;
use MyVendor\MyExtension\Repository\UserRepository;
use MyVendor\MyExtension\Logger\Logger;
abstract class AbstractController
{
protected ?Logger $logger = null;
public function injectLogger(Logger $logger)
{
$this->logger = $logger;
}
}
final class UserController extends AbstractController
{
private UserRepository $userRepository;
public function __construct(UserRepository $userRepository)
{
$this->userRepository = $userRepository;
}
}
We have an abstract constroller service with a dependency plus a controller service that extends the abstract and has further dependencies.
Now assume the abstract class is provided by TYPO3 core and the consuming class
is provided by an extension. If the abstract class would use constructor injection,
the consuming class would need to know the dependencies of the abstract, add its
own dependency to the constructor, and then call parent::__construct($logger)
to
satisfy the dependency of the abstract. This would hardcode all dependencies
of the abstract into extending classes. If later the abstract is changed and
another dependency is added to the constructor, this would break consuming
classes since they did not know that.
Differently put: When core classes "pollute" __construct()
with dependencies,
the core can not add dependencies without being breaking. This is the reason why
for example the extbase AbstractController
uses inject*()
methods for its
dependencies: Extending classes can then use constructor injection, do not need
to call parent::__construct()
, and the core is free to change dependencies of
the abstract.
In general, when the core provides abstract classes that are expected to be
extended by extensions, the abstract class should use inject*()
methods instead of
constructor injection. Extensions of course can follow this idea in similar
scenarios.
This construct has some further implications: Abstract classes should
think about making their dependency properties private
, so extending classes
can not rely on them. Furthermore, classes that should not be extended by extensions
are free to use constructor injection and should be marked final
, making
sure they can't be extended to allow internal changes.
As a last note on method injection, there is another way to do it: It is possible
to use a setFooDependency()
method if it has the annotation @required
.
This second way of method injection however is not used within the TYPO3
framework, should be avoided in general, and is just mentioned here for completeness.
Interface injection¶
Apart from constructor injection and inject*()
method injection, there is another
useful dependency injection scenario. Look at this example:
namespace MyVendor\MyExtension\Controller;
use MyVendor\MyExtension\Logger\LoggerInterface;
final class UserController extends AbstractController
{
protected LoggerInterface $logger;
public function __construct(LoggerInterface $logger)
{
$this->logger = $logger;
}
}
See the difference? We're requesting the injection of an interface and not a class! It works for both constructor and method injection. It forces the service container to look up which specific class is configured as implementation of the interface and inject an instance of it. This is the true heart of dependency injection: A consuming class no longer codes on a specific implementation, but on the signature of the interface. The framework makes sure something is injected that satisfies the interface, the consuming class does not care, it just knows about the interface methods. An instance administrator can decide to configure the framework to inject some different implementation than the default, and that's fully transparent for consuming classes.
Using container->get()¶
[WIP] Service containers provide two methods to obtain objects, first via $container->get()
,
and via DI. This is only available for services itself: Classes that are registered
as a service via configuration can use injection or $container->get()
. DI is
supported in two ways: As constructor injection, and as inject*()
method injection.
They lead to the same result, but have subtle differences. More on that later.
In general, services should use DI (constructor or method injection) to obtain dependencies.
This is what you'll most often find when looking at core implementations. However, it
is also possible to get the container injected and then use $container->get()
to instantiate services. This is useful for factory-like services where the exact name of classes is determined at runtime.
Configuration¶
Configure dependency injection in extensions¶
Extensions have to configure their classes to make use of the
dependency injection. This can be done in Configuration/Services.yaml
.
Alternatively, Configuration/Services.php
can also be used.
A basic Services.yaml
file of an extension looks like the following.
Note
Whenever the service configuration or class dependencies change, the Core
cache must be flushed in the Admin Tools > Maintenance or via the CLI
command cache:flush
to rebuild the compiled Symfony container. Flushing
all caches from the Clear cache menu does not flush the compiled Symfony
container.
services:
_defaults:
autowire: true
autoconfigure: true
public: false
MyVendor\MyExtension\:
resource: '../Classes/*'
exclude: '../Classes/Domain/Model/*'
- autowire
autowire: true
instructs the dependency injection component to calculate the required dependencies from type declarations. This works for constructor injection andinject*()
methods. The calculation generates a service initialization code which is cached in the TYPO3 Core cache.Attention
An extension does not have to use autowiring, but can wire dependencies manually in the service configuration file.
- autoconfigure
It is suggested to enable
autoconfigure: true
as this automatically adds Symfony service tags based on implemented interfaces or base classes. For example, autoconfiguration ensures that classes implementing\TYPO3\CMS\Core\SingletonInterface
are publicly available from the Symfony container and marked as shared (shared: true
).- Model exclusion
The path exclusion
exclude: '../Classes/Domain/Model/*'
excludes your models from the dependency injection container, which means you cannot inject them nor inject dependencies into them. Models are not services and therefore should not require dependency injection. Also, these objects are created by the Extbase persistence layer, which does not support the DI container.
Arguments¶
In case you turned off autowire
or need special arguments, you can
configure those as well. This means that you can set autowire: false
for
an extension, but provide the required arguments via config specifically for
the desired classes. This can be done in chronological order or by naming.
MyVendor\MyExtension\UserFunction\ClassA:
arguments:
$argA: '@TYPO3\CMS\Core\Database\ConnectionPool'
MyVendor\MyExtension\UserFunction\ClassB:
arguments:
- '@TYPO3\CMS\Core\Database\ConnectionPool'
This allows you to inject concrete objects like the Connection:
connection.pages:
class: 'TYPO3\CMS\Core\Database\Connection'
factory:
- '@TYPO3\CMS\Core\Database\ConnectionPool'
- 'getConnectionForTable'
arguments:
- 'pages'
MyVendor\MyExtension\UserFunction\ClassA:
public: true
arguments:
- '@connection.pages'
Now you can access the Connection
instance within ClassA
. This
allows you to execute your queries without further instantiation. For example,
this method of injecting objects also works with extension configurations and
with TypoScript settings.
Public¶
public: false
is a performance optimization and should therefore be set
in extensions. This settings controls which services are available through the
dependency injection container used internally by
GeneralUtility::makeInstance()
. However, some classes that need to be
public are automatically marked as public due to autoconfigure: true
being set. These classes include singletons, as they must be shared with code
that uses GeneralUtility::makeInstance()
and Extbase controllers.
What to make public¶
Instances of \TYPO3\CMS\Core\SingletonInterface
and Extbase controllers
are automatically marked as public. Some further classes must be marked as
public, too. As the Symfony documentation "Public and private services" puts
it:
Simply said: A service can be marked as private if you do not want to access it directly from your code.
Direct access includes instantiation via GeneralUtility::makeInstance()
with constructor arguments.
This means every class that is directly retrieved using
GeneralUtility::makeInstance()
and requires dependency injection
must be marked as public. Any other class which requires dependency injection
and is retrieved by dependency injection itself can be private. Instances of
\TYPO3\CMS\Core\SingletonInterface
and Extbase controllers are
automatically marked as public because they are retrieved using
GeneralUtility::makeInstance()
. More examples of classes that must be
marked as public:
Non-Extbase controllers
Classes registered in hooks
For such classes, an extension can override the global configuration
public: false
in Configuration/Services.yaml
for each affected
class:
services:
_defaults:
autowire: true
autoconfigure: true
public: false
MyVendor\MyExtension\:
resource: '../Classes/*'
exclude: '../Classes/Domain/Model/*'
MyVendor\MyExtension\UserFunction\ClassA:
public: true
With this configuration, you can use dependency injection in
\MyVendor\MyExtension\UserFunction\ClassA
when it is created, for example
in the context of a USER
TypoScript object, which would not be
possible if this class were private.
Errors resulting from wrong configuration¶
If objects that use dependency injection are not configured properly, one or
more of the following issues may result. In such a case, check whether the
class has to be configured as public: true
.
ArgumentCountError
is raised on missing dependency injection for
Constructor injection:
(1/1) ArgumentCountError
Too few arguments to function MyVendor\MyExtension\Namespace\Class::__construct(),
0 passed in typo3/sysext/core/Classes/Utility/GeneralUtility.php on line 3461 and exactly 1 expected
An Error
is thrown on missing dependency injection for
Method injection, once the dependency is used within the code:
(1/1) Error
Call to a member function methodName() on null
Dependency injection in a XCLASSed class¶
When extending an existing class (for example, an Extbase controller) using
XCLASS and injecting additional dependencies using constructor
injection, ensure that a reference to the extended class is added in the
Configuration/Services.yaml
file of the extending extension, as shown in
the example below:
TYPO3\CMS\Belog\Controller\BackendLogController: '@MyVendor\MyExtension\Controller\ExtendedBackendLogController'
Further information¶
Feature: #84112 - Symfony dependency injection for core and extbase of the TYPO3 Core .
Dependency Injection in TYPO3 - Blog Article by Daniel Goerz
Dependency Injection in "PHP The Right Way"
What is dependency injection? by Fabien Potencier