Yii Dependency Injection

PSR-11 compatible dependency injection container that's able to instantiate and configure classes resolving dependencies.

Features

• PSR-11 compatible.
• Supports property injection, constructor injection, and method injection.
• Detects circular references.
• Accepts array definitions. You can use it with mergeable configs.
• Provides optional autoload fallback for classes without explicit definition.
• Allows delegated lookup and has a composite container.
• Supports aliasing.
• Supports service providers.
• Has state resetter for long-running workers serving many requests, such as RoadRunner or Swoole.
• Supports container delegates.

Requirements

• PHP 8.1 or higher.
• Multibyte String PHP extension.

Installation

You could install the package with composer:

Using the container

Usage of the DI container is simple: You first initialize it with an array of definitions. The array keys are usually interface names. It will then use these definitions to create an object whenever the application requests that type. This happens, for example, when fetching a type directly from the container somewhere in the application. But objects are also created implicitly if a definition has a dependency on another definition.

Usually one uses a single container for the whole application. It's often configured either in the entry script such as index.php or a configuration file:

You could store the definitions in a .php file that returns an array:

You can define an object in several ways:

• In the simple case, an interface definition maps an id to a particular class.
• A full definition describes how to instantiate a class in more detail:
  • class has the name of the class to instantiate.
  • __construct() holds an array of constructor arguments.
  • The rest of the config is property values (prefixed with $) and method calls, postfixed with (). They're set/called in the order they appear in the array.
• Closures are useful if instantiation is tricky and can be better done in code. When using these, arguments are auto-wired by type. ContainerInterface could be used to get current container instance.
• If it's even more complicated, it's a good idea to move such a code into a factory and reference it as a static call.
• While it's usually not a good idea, you can also set an already instantiated object into the container.

See yiisoft/definitions for more information.

After you configure the container, you can obtain a service via get():

Note, however, that it's bad practice using a container directly. It's much better to rely on auto-wiring as provided by the Injector available from the yiisoft/injector package.

Using aliases

The DI container supports aliases via the Yiisoft\Definitions\Reference class. This way you can retrieve objects by a more handy name:

Using class aliases for specific configuration

To define another instance of a class with specific configuration, you can use native PHP class_alias():

It could be then conveniently used by type-hinting:

Composite containers

A composite container combines many containers in a single container. When using this approach, you should fetch objects only from the composite container.

Note that containers attached earlier override dependencies of containers attached later.

Using service providers

A service provider is a special class that's responsible for providing complex services or groups of dependencies for the container and extensions of existing services.

A provider should extend from Yiisoft\Di\ServiceProviderInterface and must contain a getDefinitions() and getExtensions() methods. It should only provide services for the container and therefore should only contain code related to this task. It should never implement any business logic or other functionality such as environment bootstrap or applying changes to a database.

A typical service provider could look like:

Here you created a service provider responsible for bootstrapping of a car factory with all its dependencies.

An extension is callable that returns a modified service object. In this case you get existing Garage service and put a car into the garage by calling the method setCar(). Thus, before applying this provider, you had an empty garage and with the help of the extension you fill it.

To add this service provider to a container, you can pass either its class or a configuration array in the extra config:

When you add a service provider, DI calls its getDefinitions() and getExtensions() methods immediately and both services and their extensions get registered into the container.

Container tags

You can tag services in the following way:

Now you can get tagged services from the container in the following way:

The result is an array that has two instances: BlueCarService and RedCarService.

Another way to tag services is setting tags via container constructor:

Resetting services state

Despite stateful services isn't a great practice, these are often inevitable. When you build long-running applications with tools like Swoole or RoadRunner you should reset the state of such services every request. For this purpose you can use StateResetter with resetters callbacks:

The callback has access to the private and protected properties of the service instance, so you can set the initial state of the service efficiently without creating a new instance.

You should trigger the reset itself after each request-response cycle. For RoadRunner, it would look like the following:

Setting resetters in definitions

You define the reset state for each service by providing "reset" callback in the following way:

Note: resetters from definitions work only if you don't set StateResetter in definition or service providers.

Configuring StateResetter manually

To manually add resetters or in case you use Yii DI composite container with a third party container that doesn't support state reset natively, you could configure state resetter separately. The following example is PHP-DI:

Specifying metadata for non-array definitions

To specify some metadata, such as in cases of "resetting services state" or "container tags," for non-array definitions, you could use the following syntax:

Now you've explicitly moved the definition itself to "definition" key.

Delegates

Each delegate is a callable returning a container instance that's used in case DI can't find a service in a primary container:

To configure delegates use extra config:

Tuning for production

By default, the container validates definitions right when they're set. In the production environment, it makes sense to turn it off:

Strict mode

Container may work in a strict mode, that's when you should define everything in the container explicitly. To turn it on, use the following code:

Documentation

• Internals

If you need help or have a question, the Yii Forum is a good place for that. You may also check out other Yii Community Resources.

License

The Yii Dependency Injection is free software. It is released under the terms of the BSD License. Please see LICENSE for more information.

Maintained by Yii Software.

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