zalas/injector

Injects services from a PSR-11 service container into objects

v1.2.0 2019-06-08 07:53 UTC

README

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Injects services from a PSR-11 dependency injection container into objects. Service information is read from class properties annotated with @inject, but extension points are provided to read them from any source.

Example of a class that default implementation of injector can work with:

class Foo
{
    /**
     * @var Service1
     * @inject
     */
    private $service1;

    /**
     * @Service2
     * @inject foo.service2
     */
    private $service2;
}

Why?

The library is useful in situations when we have no control over how objects are instantiated, so we can't use proper dependency injection. One use case is feeding services from an application container to integration test cases. Test cases are instantiated by a test framework, so it's not possible to provide additional dependencies during construction time. However, since test frameworks usually give ways to hook into the initialization process, it's still possible to provide additional dependencies before test cases are called.

PHPUnit integration is actually implemented in zalas/phpunit-injector (github repository: https://github.com/jakzal/phpunit-injector).

Installation

composer require zalas/injector

Usage

Properties should be annotated with @inject in order for them to be recognised by the default injector implementation:

class Foo
{
    /**
     * @var Service1
     * @inject
     */
    private $service1;

    /**
     * @Service2
     * @inject foo.service2
     */
    private $service2;

    public function hasService1(): bool
    {
        return $this->service1 instanceof Service1;
    }

    public function hasService2(): bool
    {
        return $this->service2 instanceof Service2;
    }
}

class Service1
{
}

class Service2
{
}

The injector can be used to feed services into properties of an already instantiated object:

use Zalas\Injector\Service\Injector;
use Zalas\Injector\Factory\DefaultContainerFactory;
use Zalas\Injector\Factory\DefaultExtractorFactory;

$foo = new Foo();
$container = /* create / fetch your container */;
$injector = new Injector(new DefaultContainerFactory($container), new DefaultExtractorFactory());
$injector->inject($foo);

var_dump($foo->hasService1());
// bool(true)
var_dump($foo->hasService2());
// bool(true)

Extension points

Zalas\Injector\Service\Injector injects services to objects. Services are provided by a PSR-11 container (Psr\Container\ContainerInterface). Details of services to inject are read with an extractor (Zalas\Injector\Service\Extractor).

Both collaborators are accessed via their factories (Zalas\Injector\Service\ContainerFactory and Zalas\Injector\Service\ExtractorFactory).

The injector provides two extension points:

  • container factory - allows to change the way container is created
  • extractor & extractor factory - allow to provide a custom way of extracting definitions of services to inject

Container factory

The Zalas\Injector\Factory\DefaultContainerFactory is a default factory implementation that always returns an instance of container created externally.

The Zalas\Injector\Service\ContainerFactory interface needs to be implemented to provide customised way of creating the service container to be used with injector.

Extractor & extractor factory

The default implementation of extractor (Zalas\Injector\PhpDocumentor\ReflectionExtractor) leverages phpDocumentor's reflection dockblock library for annotation parsing. It uses the @inject annotation to read service information. The annotation accepts service id as an optional value. Otherwise the type is used. Zalas\Injector\Factory\DefaultExtractorFactory creates this default implementation of extractor.

Implement the Zalas\Injector\Service\Extractor interface to support your own way of extracting definitions of services to inject. A factory that implements the Zalas\Injector\Service\ExtractorFactory will also need to be created to instantiate the custom extractor.

Contributing

Please read the Contributing guide to learn about contributing to this project. Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.