no-framework-tutorial/09-dependency-injector.md

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Dependency Injector

A dependency injector resolves the dependencies of your class and makes sure that the correct objects are injected when the class is instantiated.

Again the psr has defined an interface for dependency injection that we can work with. Almost all common dependency injection containers implement this interface, so it is a good starting point to look for a suitable solution on packagist.

I choose the PHP-DI container, as it is easy to configure and provides some very powerfull features out of the box.

After installing the container through composer create a new file with the name dependencies.php in your config folder:

<?php declare(strict_types = 1);

$builder = new \DI\ContainerBuilder();
$builder->addDefinitions([
    \Psr\Http\Message\ResponseInterface::class => \DI\create(\Laminas\Diactoros\Response::class),
    \Psr\Http\Message\ServerRequestInterface::class => fn () => \Laminas\Diactoros\ServerRequestFactory::fromGlobals(),
]);

return $builder->build();

In this file we create a containerbuilder, add some definitions to it and return the container. As the container supports autowiring we only need to define services where we want to use a specific implementation of an interface.

In the example i used two different ways of defining the service. The first is by using the 'create' method of PHP-DI to tell the container that it should create a Diactoros\Response object when ever I query a ResponseInterface, in the second exampler I choose to write a small factory closure that wraps the Laminas Requestfactory.

Make sure to read the documentation on definition types on the PHP-DI website, as we will use that extensively.

Of course your Bootstrap.php will also need to be changed. Before you were setting up $request and $response with new calls. Switch that to the dependency container. We do not need to get the response here, as the container will create and use it internally to create our Handler-Object

$container = require __DIR__ . '/../config/dependencies.php';
assert($container instanceof \Psr\Container\ContainerInterface);

$request = $container->get(\Psr\Http\Message\ServerRequestInterface::class);
assert($request instanceof \Psr\Http\Message\ServerRequestInterface);

The other part that has to be changed is the dispatching of the route. Before you had the following code:

$className = $routeInfo[1];
$handler = new $className($response);
assert($handler instanceof \Psr\Http\Server\RequestHandlerInterface)
foreach ($routeInfo[2] as $attributeName => $attributeValue) {
    $request = $request->withAttribute($attributeName, $attributeValue);
}
$response = $handler->handle($request);

Change that to the following:

/** @var RequestHandlerInterface $handler */
$className = $routeInfo[1];
$handler = $container->get($className);
assert($handler instanceof RequestHandlerInterface);
foreach ($routeInfo[2] as $attributeName => $attributeValue) {
    $request = $request->withAttribute($attributeName, $attributeValue);
}
$response = $handler->handle($request);

Make sure to use the container fetch the response object in the catch blocks as well:

} catch (MethodNotAllowed) {
    $response = $container->get(ResponseInterface::class);
    assert($response instanceof ResponseInterface);
    $response = $response->withStatus(405);
    $response->getBody()->write('Not Allowed');
} catch (NotFound) {
    $response = $container->get(ResponseInterface::class);
    assert($response instanceof ResponseInterface);
    $response = $response->withStatus(404);
    $response->getBody()->write('Not Found');
}

Now all your controller constructor dependencies will be automatically resolved with PHP-DI.

We can now use that to inject all kinds of services. Often we need to work with the Current time to do some comparisons in an application. Of course we are writing S.O.L.I.D. and testable code so that we would never be so crazy as to call $time = new \DateTimeImmutable(); in our Action directly, because then we would need to change the system time of we want to work with a different date in a test.

Therefore we are creating a new Namespace called 'Service\Time' where we introduce a Now-Interface and an Implementation that creates us a DateTimeImmutable object with the current date and time.

src/Service/Time/Now.php:

namespace Lubian\NoFramework\Service\Time;

interface Now
{
    public function __invoke(): \DateTimeImmutable;
}

src/Service/Time/SystemClockNow.php:

namespace Lubian\NoFramework\Service\Time;

final class SystemClockNow implements Now
{

    public function __invoke(): \DateTimeImmutable
    {
        return new \DateTimeImmutable;
    }
}

If we want to use that Service in our HelloAction we just need to add it as another argument for the Constructor and update the handle-method to use the new class property:

<?php declare(strict_types=1);

namespace Lubian\NoFramework\Action;

use Lubian\NoFramework\Service\Time\SystemClockNow;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Server\RequestHandlerInterface;

final class Hello implements RequestHandlerInterface
{
    public function __construct(
        private ResponseInterface $response,
        private SystemClockNow $now,
    )
    {
    }

    public function handle(ServerRequestInterface $request): ResponseInterface
    {
        $name = $request->getAttribute('name', 'Stranger');
        $nowAsString = ($this->now)()->format('H:i:s');
        $body = $this->response->getBody();

        $body->write('Hello ' . $name . '!');
        $body->write(' The Time is ' . $nowAsString);

        return $this->response
            ->withBody($body)
            ->withStatus(200);
    }
}

If you open the route in your browser you should see that the current time gets displayed. This happens because PHP-DI automatically figures out what classes are requested in the constructor and tries to create the objects needed.

But we do not want to depend on the SystemClockNow implementation in our class because that would violate our sacred S.O.L.I.D. principles therefore we need to change the Typehint to the Now interface:

    public function __construct(
        private ResponseInterface $response,
        private Now $now,
    )

When we are now accessing the Handler in the Browser we get an Error because we have not defined which implementation should be use to satisfy dependencies on the Now interface. So lets add that definition to our dependencies file:

\Lubian\NoFramework\Service\Time\Now::class => fn () => new \Lubian\NoFramework\Service\Time\SystemClockNow(),

we could also use the PHP-DI create method to delegate the object creation to the container implementation:

\Lubian\NoFramework\Service\Time\Now::class => DI\create(\Lubian\NoFramework\Service\Time\SystemClockNow::class),

this way the container can try to resolve any dependencies that the class might have internally, but prefer the other method because we are not depending on this specific dependency injection implementation.

Either way the container should now be able to correctly resolve the dependency on the Now interfacen when you are requesting the Hello action.

If you run phpstan now, you will get some errors, because the get method on the ContainerInterface returns 'mixed'. As we will adress these issues later, lets tell phpstan that we know about the issue and we can ignore it for now. This way we wont get any warnings for this particular issue, but for any other issues we add to our code.

Update the phpstan.neon file to include a "baseline" file:

includes:
    - phpstan-baseline.neon

parameters:
    level: 9
    paths:
        - src

if we run phpstan with './vendor/bin/phpstan analyse --generate-baseline' it will add all current errors to that file and ignore them in the future. You can also add that command to your composer.json for easier access. I have called it just 'baseline'

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