Autowiring services

GraphQLite can automatically inject services in your fields/queries/mutations signatures.

Some of your fields may be computed. In order to compute these fields, you might need to call a service.

Most of the time, your @Type annotation will be put on a model. And models do not have access to services. Hopefully, if you add a type-hinted service in your field's declaration, GraphQLite will automatically fill it with the service instance.

Sample

Let's assume you are running an international store. You have a Product class. Each product has many names (depending on the language of the user).

namespace App\Entities;

use TheCodingMachine\GraphQLite\Annotations\Autowire;
use TheCodingMachine\GraphQLite\Annotations\Field;
use TheCodingMachine\GraphQLite\Annotations\Type;

use Symfony\Component\Translation\TranslatorInterface;

/**
 * @Type()
 */
class Product
{
    // ...

    /**
     * @Field()
     * @Autowire(for="$translator")
     */
    public function getName(TranslatorInterface $translator): string
    {
        return $translator->trans('product_name_'.$this->id);
    }
}

When GraphQLite queries the name, it will automatically fetch the translator service.

As with most autowiring solutions, GraphQLite assumes that the service identifier in the container is the fully qualified class name of the type-hint. So in the example above, GraphQLite will look for a service whose name is Symfony\Component\Translation\TranslatorInterface.

Best practices

It is a good idea to refrain from type-hinting on concrete implementations. Most often, your field declaration will be in your model. If you add a type-hint on a service, you are binding your domain with a particular service implementation. This makes your code tightly coupled and less testable.

Please don't do that:

    /** * @Field() */ public function getName(MyTranslator $translator): string

Instead, be sure to type-hint against an interface.

Do this instead:

    /** * @Field() */ public function getName(TranslatorInterface $translator): string

By type-hinting against an interface, your code remains testable and is decoupled from the service implementation.

Fetching a service by name (discouraged!)

Optionally, you can specify the identifier of the service you want to fetch from the controller:

/**
 * @Autowire(for="$translator", identifier="translator")
 */

While GraphQLite offers the possibility to specify the name of the service to be autowired, we would like to emphasize that this is highly discouraged. Hard-coding a container identifier in the code of your class is akin to using the "service locator" pattern, which is known to be an anti-pattern. Please refrain from doing this as much as possible.

Alternative solution

You may find yourself uncomfortable with the autowiring mechanism of GraphQLite. For instance maybe:

• Your service identifier in the container is not the fully qualified class name of the service (this is often true if you are not using a container supporting autowiring)
• You do not want to inject a service in a domain object
• You simply do not like the magic of injecting services in a method signature

If you do not want to use autowiring and if you still need to access services to compute a field, please read on the next chapter to learn how to extend a type.