index.md

Events

Events are a way to hook into the execution flow. This bundle provides various events from executor and context value initialization, executor result formatting (data, errors, extensions), errors/warnings formatting.

With this in mind we now turn to explain each one of them.

Executor context value

Event: graphql.executor.context

This event can be listen to initialize executor contextValue argument.

Executor initialisation

Event: graphql.pre_executor

This event can be listen to initialize executor execute arguments (schema, requestString, rootValue, contextValue, variableValue, operationName).

For example:

• Initializing rootValue with the current user (we assume that user is fully authenticated)

  App\EventListener\RootValueInitialization:
      tags:
          - { name: kernel.event_listener, event: graphql.pre_executor, method: onPreExecutor }

  <?php
  
  namespace App\EventListener;
  
  use Overblog\GraphQLBundle\Event\ExecutorArgumentsEvent;
  use Symfony\Component\Security\Core\Authentication\Token\TokenInterface;
  
  class RootValueInitialization
  {
    private $token;
  
    public function __construct(TokenInterface $token)
    {
         $this->token = $token;
    }
  
    public function onPreExecutor(ExecutorArgumentsEvent $event)
    {
        $event->setRootValue($this->token->getUser());
    }
  }

Executor result

Event: graphql.post_executor

This event can be listen to set custom error handling and formatting, it can also be use to add information to extensions section.

For example:

• How to add credits entry in extensions section

  App\EventListener\Credits:
      tags:
          - { name: kernel.event_listener, event: graphql.post_executor, method: onPostExecutor }

  <?php
  
  namespace App\EventListener;
  
  use Overblog\GraphQLBundle\Event\ExecutorResultEvent;
  
  class Credits
  {
    public function onPostExecutor(ExecutorResultEvent $event)
    {
        $event->getResult()->extensions['credits'] = 'This api was powered by "OverblogGraphQLBundle".';
    }
  }

  result:

  {
    "data": {"foo": "bar"},
    "extensions": {
      "credits": "This api was powered by \"OverblogGraphQLBundle\"."
    }
  }

Error formatting

Event: graphql.error_formatting

This event can be listen to add or remove fields from result errors and extensions.warnings sections, it can also be use to log errors or exception. Each single error or warning will trigger an event.

For example:

• How to add error code:

  App\EventListener\ErrorCode:
      tags:
          - { name: kernel.event_listener, event: graphql.error_formatting, method: onErrorFormatting }

  <?php
  
  namespace App\EventListener;
  
  use Overblog\GraphQLBundle\Event\ErrorFormattingEvent;
  
  class ErrorCode
  {
    public function onErrorFormatting(ErrorFormattingEvent $event)
    {
        $error = $event->getError();
        if ($error->getPrevious()) {
            $code = $error->getPrevious()->getCode();
        } else {
            $code = $error->getCode();
        }
        $formattedError = $event->getFormattedError();
        $formattedError->offsetSet('code', $code); // or $formattedError['code'] = $code;
    }
  }

  result:

  {
    "data": null,
    "errors": [
      {
        "code": 123,
        "category": "internal",
        "message": "Internal server Error"
      }
    ]
  }

Note:

• This event is dispatch by this bundle default error handler, that the reason why, disabling error handler will also disable this event.