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 is pretty simple:

public function process(array $params, callable $next)

$params is an arbitrary array of data, much like an event object passed to an event handler. The $next parameter refers to the next middleware in the chain.

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

class LoggingMiddleware implements Middleware
{
    public function process(array $params, callable $next)
    {
        $query = $params['query'];
        Injector::inst()->get(LoggerInterface::class)
        	->info('Query executed: ' . $query);
        
        // 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'