Do I need to define a container inside a class for dependency injection?

Question

I am learning Auraphp Di, and I want to write sample code. Suppose I have these files:

public/index.php:

use Aura\Di\ContainerBuilder;
use MyPackage\Component\Authentication\AuthenticateFlow;

require_once dirname(__DIR__) . '/vendor/autoload.php';

$builder = new ContainerBuilder();
$di = $builder->newInstance();

$di->set('authenticateFlow', $di->lazyNew(AuthenticateFlow::class));

$authenticateFlow = $di->get('authenticateFlow');

$authenticateFlow->showName('Belkin');

/src/Components/Authentication/AuthenticationFlow.php:

namespace MyPackage\Components\Authentication;

class AuthenticationFlow
{
    public function showName($name)
    {
        echo $name;
    }
}

This is working fine. Now suppose I have another class (/src/Components/Authentication/Filter.php), which has a method called filterInput:

namespace MyPackage\Components\Authentication;

class Filter
{
    public function filterInput($input)
    {
        return htmlspecialchars($input);
    }
}

How can I inject Filter to AuthenticationFlow, to use filterInput() method? I wanna have something like this in AuthenticationFlow::showName():

echo $this->filter->filterInput($name);

I am aware that I need to inject Filter class in AuthenticationFlow constructor, but I don't know if I can use the container built in the index.php or not. If I need to create another container in AuthenticationFlow, how index.php would be aware of it?

Answer 1

Your application need to make use of the di container heavily in-order to inject the necessary dependencies. This is not the case of Aura.

Let us step back and look what you would do if you don't use a container.

In-order to make use of Filter object inside AuthenticationFlow, you need to inject the Filter object either via constructor or a setter method. In the example below I am making use of constructor injection.

class AuthenticationFlow
{
    protected $filter;

    public function __construct(Filter $filter)
    {
        $this->filter = $filter;
    }

    public function showName($name)
    {
        return $this->filter->filterInput($name);
    }
}

So you will create an object of AuthenticationFlow as below.

$auth = new AuthenticationFlow(new Filter);

In the case of Aura.Di, you may do something like

$object = $di->newInstance(AuthenticateFlow::class);

If auto resolution is turned off, you need to define dependencies as below

$di->params[AuthenticateFlow::class]['filter'] = $di->lazyNew(Filter::class);

This will not be true, in an application. You may need AuthenticateFlow on a different HelloController::class.

Class HelloController
{
    protected $auth;

    public function __construct(AuthenticationFlow $auth)
    {
        $this->auth = $auth;
    }

    public function execute()
    {
        // Do something 
    }
}

So in that case, HelloController::class need to be instantiated via the di itself. Else the dependencies will not be injected automatically.

$object = $di->newInstance(HelloController::class);

You can extend the Aura\Di\ContainerConfig and define services in multiple classes.

Example :

namespace YourVendor;

use Aura\Di\Container;
use Aura\Di\ContainerConfig;
class Config extends ContainerConfig
{
    public function define(Container $di)
    {
        $di->set(HelloController::class, $di->lazyNew(HelloController::class));
        $di->params[HelloController::class]['auth'] = $di->lazyNew(AuthenticateFlow::class);
        $di->params[AuthenticateFlow::class]['filter'] = $di->lazyNew(Filter::class);
    }

    public function modify(Container $di)
    {
        // You can get the service and modify if needed
        // $auth = $di->get('authenticateFlow');
    }
}

Now your index.php will look like,

require_once dirname(__DIR__) . '/vendor/autoload.php';

$builder = new ContainerBuilder();
$di = $container_builder->newConfiguredInstance([
    'YourVendor\Config',    
]);

$hello = $di->newInstance(HelloController::class);
$hello->execute();

As I mentioned in previous answer, I recommend you go through the docs first. It will really help you in long run.