silverstripe-framework/docs/en/02_Developer_Guides/19_GraphQL/06_extending/adding_middleware.md

title	summary
Adding middleware	Add middleware to to extend query execution

Extending the schema

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Adding middleware

Middleware is any piece of functionality that is interpolated into a larger process. A key feature of middleware is that it can be used with other middlewares in sequence and not have to worry about the order of execution.

In silverstripe-graphql, middleware is used for query execution, but could ostensibly be used elsewhere too if the API ever accomodates such an expansion.

[notice] The middleware API in the silverstripe-graphql module is separate from other common middleware APIs in Silverstripe CMS, such as HTTPMiddleware. [/notice]

The signature for middleware looks like this:

public function process(Schema $schema, $query, $context, $vars, callable $next)

• $schema: The underlying Schema object. Useful to inspect whether types are defined in a schema.
• $query: The raw query string.
• $context: An arbitrary array which holds information shared between resolvers. Use implementors of SilverStripe\GraphQL\Schema\Interfaces\ContextProvider to get and set data, rather than relying on the array keys directly.
• $vars: An array of (optional) Query Variables.
• $next: A callable referring to the next middleware in the chain

Let's write a simple middleware that logs our queries as they come in.

use SilverStripe\GraphQL\QueryHandler\UserContextProvider;
use GraphQL\Type\Schema;

class LoggingMiddleware implements Middleware
{
    public function process(Schema $schema, $query, $context, $vars, callable $next)
    {
        $member = UserContextProvider::get($context);
        
        Injector::inst()->get(LoggerInterface::class)
        	->info(sprintf(
                'Query executed: %s by %s',
                $query,
                $member ? $member->Title : '<anonymous>';
            ));
        
        // Hand off execution to the next middleware
        return $next($params);
    }
}

Now we can register the middleware with our query handler:

  SilverStripe\GraphQL\QueryHandler\QueryHandlerInterface.default:
    class: SilverStripe\GraphQL\QueryHandler\QueryHandler
    properties:
      Middlewares:
        logging: '%$MyProject\Middleware\LoggingMiddleware'