Sometimes we need to retrieve some kind of handler class that depending on an attribute is different.

Thanks to Factory pattern we can solve this scenario in an elegant way... but we can improve it through the Service Container.

In this case we are going to see how to do it with Symfony Service Container, but this could be achieved by any other Service Container implementation.

Example scenario

Let's imagine a (more or less) real situation and work with it: We have an endpoint that depending on payload parameter "channel", we will send a "message" through different possible communication channels (email, sms, letter...).

To make things easier, we will do not cover additional parameters as to or phone_number etc.

Example payload:

{
  "channel": "email",
  "message": "Hello world"
}

Using a simple factory

The easiest way to solve this is creating a factory class that solves that logic:

final class ChannelFactory
{
    public static function create(string $type): ChannelInterface
    {
      switch($type) {
        case 'email':
          return new EmailChannelHandler();
        break;
        case 'sms':
          return new SmsChannelHandler();
        break;
      }

      throw new InvalidArgumentException('Unknown channel given');
    }
}

Pros

• Easy to read if only 2 or 3 different types

Cons

• Difficult to read if lot of types
• You have to add code to add a new type

Using a simple factory through service container

Let's make it more scalable and maintainable!

We can have an array of compatible handlers and decide which one is the correct. You need to add the related type to the Channel handler with some method like getType().

final class ChannelFactory
{
    public function __construct(private ChannelInterface ...$channels)
    {
    }

    public function create(string $type): ChannelInterface
    {
      foreach($this->channels as $channel) {
        if ($type === $channel::getType()) {
          return new $channel;
        }
      }

      throw new InvalidArgumentException('Unknown channel given');
    }
}

And now, in our services.yml file we initialize it as follows:

App\ChannelFactory:
    arguments:
      - App\EmailChannelHandler
      - App\SmsChannelHandler

Pros

• You can add as many handlers as you want without changing php code
• Easy to add new handlers

Cons

• Maybe a little bit less easy to read for a noob

Conclusion

Service Container is a pattern really powerful and nowadays we have some amazing implementations that can help us a lot.

It's worth to use them and give to our application more flexibility even adding a little complexity for newcomers.

Updated! (2022-03-07)

As Valentin Silvestre suggested, there is a better way to set up the container to make it even more automagically:

_instanceof:
        App\ChannelHandlerInterface:
            tags: ['app.channel_handler']

App\ChannelFactory:
    arguments:
      - !tagged_iterator app.channel_handler

This is an awesome way to tell to service container that all implementations of ChannelHandlerInterface should be loaded in our factory, so we don't need to write each one in a list.

Thanks Valentin!