Configuring the service manager

The Service Manager component can be configured by passing an associative array to the component's constructor. The following keys are:

  • services: associative array that maps a key to a service instance.
  • invokables: an associative array that maps a key to a constructor-less service; i.e., for services that do not require arguments to the constructor. The key and service name usually are the same; if they are not, the key is treated as an alias.
  • factories: associative array that map a key to a factory name, or any callable.
  • abstract_factories: a list of abstract factories classes. An abstract factory is a factory that can potentially create any object, based on some criterias.
  • delegators: an associative array that maps service keys to lists of delegator factory keys, see the delegators documentation for more details.
  • aliases: associative array that map a key to a service key (or another alias).
  • initializers: a list of callable or initializers that are run whenever a service has been created.
  • lazy_services: configuration for the lazy service proxy manager, and a class map of service:class pairs that will act as lazy services; see the lazy services documentation for more details.
  • shared: associative array that maps a service name to a boolean, in order to indicate to the service manager whether or not it should cache services it creates via get method, independent of the shared_by_default setting.
  • shared_by_default: boolean that indicates whether services created through the get method should be cached. This is true by default.

Here is an example of how you could configure a service manager:

use Zend\ServiceManager\ServiceManager;

$serviceManager = new ServiceManager([
    'services'           => [],
    'invokables'         => [],
    'factories'          => [],
    'abstract_factories' => [],
    'delegators'         => [],
    'aliases'            => [],
    'initializers'       => [],
    'lazy_services'      => [],
    'shared'             => [],
    'shared_by_default'  => true,
]);

Factories

A factory is any callable or any class that implements the interface Zend\ServiceManager\Factory\FactoryInterface.

Service manager components provide a default factory that can be used to create objects that do not have any dependencies:

use Zend\ServiceManager\Factory\InvokableFactory;
use Zend\ServiceManager\ServiceManager;
use stdClass;

$serviceManager = new ServiceManager([
    'factories' => [
        MyObject::class => MyObjectFactory::class,
    ],
]);

For invokable classes we can use Zend\ServiceManager\Factory\InvokableFactory but for performance reasons using invokables configuration is recommended.

As said before, a factory can also be a callable, to create more complex objects:

use Interop\Container\ContainerInterface;
use Zend\ServiceManager\Factory\InvokableFactory;
use Zend\ServiceManager\ServiceManager;
use stdClass;

$serviceManager = new ServiceManager([
    'factories' => [
        stdClass::class => InvokableFactory::class,
        MyObject::class => function(ContainerInterface $container, $requestedName) {
            $dependency = $container->get(stdClass::class);
            return new MyObject($dependency);
        },
    ],
]);

Each factory always receive a ContainerInterface argument (this is the base interface that the ServiceManager implements), as well as the requested name as the second argument. In this case, the $requestedName is MyObject.

Alternatively, the above code can be replaced by a factory class instead of a closure. This leads to more readable code. For instance:

// In MyObjectFactory.php file

class MyObjectFactory implements FactoryInterface
{
    public function __invoke(ContainerInterface $container, $requestedName, array $options = null)
    {
        $dependency = $container->get(stdClass::class);
        return new MyObject($dependency);
    }
}

// or without implementing the interface:
class MyObjectFactory
{
    public function __invoke(ContainerInterface $container, $requestedName)
    {
        $dependency = $container->get(Dependency::class);
        return new MyObject($dependency);
    }
}

// When creating the service manager:
$serviceManager = new ServiceManager([
    'factories' => [
        stdClass::class => InvokableFactory::class,
        MyObject::class => MyObjectFactory::class
    ]
]);

For performance reasons, factories objects are not created until requested. In the above example, this means that the MyObjectFactory object won't be created until MyObject is requested.

Mapping multiple service to the same factory

Unlike version 2 implementations of the component, in the version 3 implementation, the $requestedName is guaranteed to be passed as the second parameter of a factory. This is useful when you need to create multiple services that are created exactly the same way, hence reducing the number of needed factories.

For instance, if two services share the same creation pattern, you could attach the same factory:

// In MyObjectFactory.php file

class MyObjectFactory implements FactoryInterface
{
    public function __invoke(ContainerInterface $container, $requestedName, array $options = null)
    {
        $dependency = $container->get(stdClass::class);
        return new $requestedName($dependency);
    }
}

// or without implementing the interface:
class MyObjectFactory
{
    public function __invoke(ContainerInterface $container, $requestedName)
    {
        $dependency = $container->get(Dependency::class);
        return new $requestedName($dependency);
    }
}

// When creating the service manager:
$serviceManager = new ServiceManager([
    'factories' => [
        MyObjectA::class => MyObjectFactory::class,
        MyObjectB::class => MyObjectFactory::class
    ]
]);

This pattern can often replace abstract factories, and is more performant:

  • Lookups for services do not need to query abstract factories; the service is mapped explicitly.
  • Once the factory is loaded for any object, it stays in memory for any other service using the same factory.

Using factories is recommended in most cases where abstract factories were used in version 2.

This feature can be abused, however: for instance, if you have dozens of services that share the same creation, but which do not share any common functionality, we recommend to create separate factories.

Abstract factories

An abstract factory is a specialized factory that can be used to create any service, if it has the capability to do so. An abstract factory is often useful when you do not know in advance the name of the service (e.g. if the service name is generated dynamically at runtime), but know that the services share a common creation pattern.

An abstract factory must be registered inside the service manager, and is checked if no factory can create an object. Each abstract factory must implement Zend\ServiceManager\Factory\AbstractFactoryInterface:

// In MyAbstractFactory.php:

class MyAbstractFactory implements AbstractFactoryInterface
{
    public function canCreate(ContainerInterface $container, $requestedName)
    {
        return in_array('Traversable', class_implements($requestedName), true);
    }

    public function __invoke(ContainerInterface $container, $requestedName, array $options = null)
    {
        return $requestedName();
    }
}

// When creating the service manager:
$serviceManager = new ServiceManager([
    'abstract_factories' => [
        new MyAbstractFactory() // You could also pass a class name: MyAbstractFactory::class
    ]
]);

// When fetching an object:
$object = $serviceManager->get(A::class);

Here is what will happen:

  1. The service manager will check if it contains a factory mapped to the A::class service.
  2. Because none is found, it will process each abstract factory, in the order in which they were registered.
  3. It will call the canCreate() method, passing the service manager instance and the name of the requested object. The method can use any logic whatsoever to determine if it can create the service (such as checking its name, checking for a required dependency in the passed container, checking if a class implements a given interface, etc.).
  4. If canCreate() returns true, it will call the __invoke method to create the object. Otherwise, it will continue iterating the abstract factories, until one matches, or the queue is exhausted.

Best practices

While convenient, we recommend you to limit the number of abstract factories. Because the service manager needs to iterate through all registered abstract factories to resolve services, it can be costly when multiple abstract factories are present.

Often, mapping the same factory to multiple services can solve the issue more efficiently (as described in the Factories section).

Aliases

An alias provides an alternative name for a registered service.

An alias can also be mapped to another alias (it will be resolved recursively). For instance:

use Zend\ServiceManager\Factory\InvokableFactory;
use Zend\ServiceManager\ServiceManager;
use stdClass;

$serviceManager = new ServiceManager([
    'factories' => [
        stdClass::class => InvokableFactory::class
    ],

    'aliases' => [
        'A' => stdClass::class,
        'B' => 'A'
    ]
]);

$object = $serviceManager->get('B');

In this example, asking B will be resolved to A, which will be itself resolved to stdClass::class, which will finally be constructed using the provided factory.

Best practices

We recommend you minimal use of aliases, and instead using the ::class language construct to map using a FQCN (Fully-Qualified-Class-Name). This provides both better discoverability within your code, and allows simpler refactoring, as most modern IDEs can refactor class names specified using the ::class keyword.

Initializers

An initializer is any callable or any class that implements the interface Zend\ServiceManager\Initializer\InitializerInterface. Initializers are executed for each service the first time they are created, and can be used to inject additional dependencies.

For instance, if we'd want to automatically inject the dependency EventManager::class in all objects that implement the interface EventManagerAwareInterface, we could create the following initializer:

use Interop\Container\ContainerInterface;
use stdClass;
use Zend\ServiceManager\ServiceManager;

$serviceManager = new ServiceManager([
    'initializers' => [
        function(ContainerInterface $container, $instance) {
            if (! $instance instanceof EventManagerAwareInterface) {
                return;
            }
            $instance->setEventManager($container->get(EventManager::class));
        }
    ]
]);

Alternately, you can create a class that implements Zend\ServiceManager\Initializer\InitializerInterface, and pass it to the initializers array:

// In MyInitializer.php

class MyInitializer implements InitializerInterface
{
    public function __invoke(ContainerInterface $container, $instance)
    {
        if (! $instance instanceof EventManagerAwareInterface) {
            return;
        }
        $instance->setEventManager($container->get(EventManager::class));
    }
}

// When creating the service manager:

use Interop\Container\ContainerInterface;
use stdClass;
use Zend\ServiceManager\ServiceManager;

$serviceManager = new ServiceManager([
    'initializers' => [
        new MyInitializer() // You could also use MyInitializer::class
    ]
]);

Note that initializers are automatically created when the service manager is initialized, even if you pass a class name.

Best practices

While convenient, initializer usage is also problematic. They are provided primarily for backwards compatibility, but we highly discourage their usage.

The primary issues with initializers are:

  • They lead to fragile code. Because the dependency is not injected directly in the constructor, it means that the object may be in an "incomplete state". If for any reason the initializer is not run (if it was not correctly registered for instance), bugs ranging from the subtle to fatal can be introduced.

Instead, we encourage you to inject all necessary dependencies via the constructor, using factories. If some dependencies use setter or interface injection, use delegator factories.

If a given service has too many dependencies, then it may be a sign that you need to split this service into smaller, more focused services.

  • They are slow: an initializer is run for EVERY instance you create through the service manager. If you have ten initializers or more, this can quickly add up!

Shared

By default, a service created is shared. This means that calling the get() method twice for a given service will return exactly the same service. This is typically what you want, as it can save a lot of memory and increase performance:

$serviceManager = new ServiceManager([
    'factories' => [
        stdClass::class => InvokableFactory::class
    ]
]);

$object1 = $serviceManager->get(stdClass::class);
$object2 = $serviceManager->get(stdClass::class);

var_dump($object1 === $object2); // prints "true"

However, occasionally you may require discrete instances of a service. To enable this, you can use the shared key, providing a boolean false value for your service, as shown below:

$serviceManager = new ServiceManager([
    'factories' => [
        stdClass::class => InvokableFactory::class
    ],
    'shared' => [
        stdClass::class => false
    ]
]);

$object1 = $serviceManager->get(stdClass::class);
$object2 = $serviceManager->get(stdClass::class);

var_dump($object1 === $object2); // prints "false"

Alternately, you can use the build() method instead of the get() method. The build() method works exactly the same as the get method, but never caches the service created, nor uses a previously cached instance for the service.

$serviceManager = new ServiceManager([
    'factories' => [
        stdClass::class => InvokableFactory::class
    ]
]);

$object1 = $serviceManager->build(stdClass::class);
$object2 = $serviceManager->build(stdClass::class);

var_dump($object1 === $object2); // prints "false"

Finally, you could also decide to disable caching by default (even when calling the get() method), by setting the shared_by_default option to false:

$serviceManager = new ServiceManager([
    'factories' => [
        stdClass::class => InvokableFactory::class
    ],
    'shared_by_default' => false,
]);

$object1 = $serviceManager->get(stdClass::class);
$object2 = $serviceManager->get(stdClass::class);

var_dump($object1 === $object2); // prints "false"

Passing config to a factory/delegator

So far, we have covered examples where services are created through factories (or abstract factories). The factory is able to create the object itself.

Occasionally you may need to pass additional options that act as a "context". For instance, we could have a StringLengthValidator service registered. However, this validator can have multiple options, such as min and max. Because this is dependant on the caller context (or might even be retrieved from a database, for instance), the factory cannot know what options to give when constructing the validator.

To solve this issue, the service manager offers a build() method. It works similarly to the get() method, with two main differences:

  • Services created with the build() method are never cached, nor pulled from previously cached instances for that service.
  • build() accepts an optional secondary parameter, an array of options.

Those options are transferred to all factories, abstract factories, and delegators. For instance:

// In StringLengthValidatorFactory.php

class StringLengthValidatorFactory implements FactoryInterface
{
    public function __invoke(ContainerInterface $container, $requestedName, array $options = [])
    {
        return new StringLengthValidator($options);
    }
}

// When creating the service manager:
$serviceManager = new ServiceManager([
    'factories' => [
        StringLengthValidator::class => StringLengthValidatorFactory::class
    ]
]);

// When creating the objects:

$validator1 = $serviceManager->build(StringLengthValidator::class, ['min' => 5]);
$validator2 = $serviceManager->build(StringLengthValidator::class, ['min' => 15]);

In our previous example, because the StringLengthValidator does not have any other dependencies other than the $options, we could remove the factory, and simply map it to the built-in InvokableFactory factory:

// When creating the service manager:
$serviceManager = new ServiceManager([
    'factories' => [
        StringLengthValidator::class => InvokableFactory::class
    ]
]);

// When creating the objects:

$validator1 = $serviceManager->build(StringLengthValidator::class, ['min' => 5]);
$validator2 = $serviceManager->build(StringLengthValidator::class, ['min' => 15]);

This works because the InvokableFactory will automatically pass the options (if any) to the constructor of the created object.

Altering a service manager's config

Assuming that you have not called $container->setAllowOverride(false), you can, at any time, configure the service manager with new services using any of the following methods:

  • configure(), which accepts the same configuration array as the constructor.
  • setAlias($alias, $target)
  • setInvokableClass($name, $class = null); if no $class is passed, the assumption is that $name is the class name.
  • setFactory($name, $factory), where $factory can be either a callable factory or the name of a factory class to use.
  • mapLazyService($name, $class = null), to map the service name $name to $class; if the latter is not provided, $name is used for both sides of the map.
  • addAbstractFactory($factory), where $factory can be either a Zend\ServiceManager\Factory\AbstractFactoryInterface instance or the name of a class implementing the interface.
  • addDelegator($name, $factory), where $factory can be either a callable delegator factory, or the name of a delegator factory class to use.
  • addInitializer($initializer), where $initializer can be either a callable initializer, or the name of an initializer class to use.
  • setService($name, $instance)
  • setShared($name, $shared), where $shared is a boolean flag indicating whether or not the named service should be shared.

As examples:

use Zend\ServiceManager\ServiceManager;

$serviceManager = new ServiceManager([
    'factories' => [
        stdClass::class => InvokableFactory::class;
    ]
]);

$serviceManager->configure([
    'factories' => [
        DateTime::class => InvokableFactory::class
    ]
]);

var_dump($newServiceManager->has(DateTime::class)); // prints true

// Create an alias from 'Date' to 'DateTime'
$serviceManager->setAlias('Date', DateTime::class);

// Set a factory for the 'Time' service
$serviceManager->setFactory('Time', function ($container) {
    return $container->get(DateTime::class);
});

// Map a lazy service named 'localtime' to the class DateTime.
$serviceManager->mapLazyService('localtime', DateTime::class);

// Add an abstract factory
$serviceManager->addAbstractFactory(new CustomAbstractFactory());

// Add a delegator factory for the DateTime service
$serviceManager->addDelegator(DateTime::class, function ($container, $name, $callback) {
    $dateTime = $callback();
    $dateTime->setTimezone(new DateTimezone('UTC'));
    return $dateTime;
});

// Add an initializer
// Note: don't do this. Use delegator factories instead.
$serviceManager->addInitializer(function ($service, $instance) {
    if (! $instance instanceof DateTime) {
        return;
    }
    $instance->setTimezone(new DateTimezone('America/Chicago'));
})

// Explicitly map a service name to an instance.
$serviceManager->setService('foo', new stdClass);

// Mark the DateTime service as NOT being shared.
$serviceManager->setShared(DateTime::class, false);

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