Adding custom annotations with Field middlewares

Available in GraphQLite 4.0+

Just like the @Logged or @Right annotation, you can develop your own annotation that extends/modifies the behaviour of a field/query/mutation.

If you want to create an annotation that targets a single argument (like @AutoWire(for="$service")), you should rather check the documentation about custom argument resolving

Field middlewares

GraphQLite is based on the Webonyx/Graphql-PHP library. In Webonyx, fields are represented by the FieldDefinition class. In order to create a FieldDefinition instance for your field, GraphQLite goes through a series of "middlewares".

Each middleware is passed a TheCodingMachine\GraphQLite\QueryFieldDescriptor instance. This object contains all the parameters used to initialize the field (like the return type, the list of arguments, the resolver to be used, etc...)

Each middleware must return a GraphQL\Type\Definition\FieldDefinition (the object representing a field in Webonyx/GraphQL-PHP).

/**
 * Your middleware must implement this interface.
 */
interface FieldMiddlewareInterface
{
    public function process(QueryFieldDescriptor $queryFieldDescriptor, FieldHandlerInterface $fieldHandler): ?FieldDefinition;
}

class QueryFieldDescriptor
{
    public function getName() { /* ... */ }
    public function setName(string $name)  { /* ... */ }
    public function getType() { /* ... */ }
    public function setType($type): void  { /* ... */ }
    public function getParameters(): array  { /* ... */ }
    public function setParameters(array $parameters): void  { /* ... */ }
    public function getPrefetchParameters(): array  { /* ... */ }
    public function setPrefetchParameters(array $prefetchParameters): void  { /* ... */ }
    public function getPrefetchMethodName(): ?string { /* ... */ }
    public function setPrefetchMethodName(?string $prefetchMethodName): void { /* ... */ }
    public function setCallable(callable $callable): void { /* ... */ }
    public function setTargetMethodOnSource(?string $targetMethodOnSource): void { /* ... */ }
    public function isInjectSource(): bool { /* ... */ }
    public function setInjectSource(bool $injectSource): void { /* ... */ }
    public function getComment(): ?string { /* ... */ }
    public function setComment(?string $comment): void { /* ... */ }
    public function getMiddlewareAnnotations(): MiddlewareAnnotations { /* ... */ }
    public function setMiddlewareAnnotations(MiddlewareAnnotations $middlewareAnnotations): void { /* ... */ }
    public function getOriginalResolver(): ResolverInterface { /* ... */ }
    public function getResolver(): callable { /* ... */ }
    public function setResolver(callable $resolver): void { /* ... */ }
}

The role of a middleware is to analyze the QueryFieldDescriptor and modify it (or to directly return a FieldDefinition).

If you want the field to purely disappear, your middleware can return null.

Annotations parsing

Take a look at the QueryFieldDescriptor::getMiddlewareAnnotations().

It returns the list of annotations applied to your field that implements the MiddlewareAnnotationInterface.

Let's imagine you want to add a @OnlyDebug annotation that displays a field/query/mutation only in debug mode (and hides the field in production). That could be useful, right?

First, we have to define the annotation. Annotations are handled by the great doctrine/annotations library (for PHP 7+) and/or by PHP 8 attributes.

OnlyDebug.php

namespace App\Annotations;

use Attribute;
use TheCodingMachine\GraphQLite\Annotations\MiddlewareAnnotationInterface;

/**
 * @Annotation
 * @Target({"METHOD", "ANNOTATION"})
 */
#[Attribute(Attribute::TARGET_METHOD)]
class OnlyDebug implements MiddlewareAnnotationInterface
{
}

Apart from being a classical annotation/attribute, this class implements the MiddlewareAnnotationInterface. This interface is a "marker" interface. It does not have any methods. It is just used to tell GraphQLite that this annotation is to be used by middlewares.

Now, we can write a middleware that will act upon this annotation.

namespace App\Middlewares;

use App\Annotations\OnlyDebug;
use TheCodingMachine\GraphQLite\Middlewares\FieldMiddlewareInterface;
use GraphQL\Type\Definition\FieldDefinition;
use TheCodingMachine\GraphQLite\QueryFieldDescriptor;

/**
 * Middleware in charge of hiding a field if it is annotated with @OnlyDebug and the DEBUG constant is not set
 */
class OnlyDebugFieldMiddleware implements FieldMiddlewareInterface
{
    public function process(QueryFieldDescriptor $queryFieldDescriptor, FieldHandlerInterface $fieldHandler): ?FieldDefinition
    {
        $annotations = $queryFieldDescriptor->getMiddlewareAnnotations();

        /**
         * @var OnlyDebug $onlyDebug
         */
        $onlyDebug = $annotations->getAnnotationByType(OnlyDebug::class);

        if ($onlyDebug !== null && !DEBUG) {
            // If the onlyDebug annotation is present, returns null.
            // Returning null will hide the field.
            return null;
        }

        // Otherwise, let's continue the middleware pipe without touching anything.
        return $fieldHandler->handle($queryFieldDescriptor);
    }
}

The final thing we have to do is to register the middleware.

• Assuming you are using the SchemaFactory to initialize GraphQLite, you can register the field middleware using:

  $schemaFactory->addFieldMiddleware(new OnlyDebugFieldMiddleware());

• If you are using the Symfony bundle, you can register your field middleware services by tagging them with the graphql.field_middleware tag.