---
title: Adding middleware
summary: Add middleware to to extend query execution
---
# Extending the schema

[CHILDREN asList]

[alert]
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Help us improve it by joining #graphql on the [Community Slack](https://www.silverstripe.org/blog/community-slack-channel/),
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Docs for the current stable version (3.x) can be found
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[/alert]

## 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:

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

 * `$schema`: The underlying [Schema](http://webonyx.github.io/graphql-php/type-system/schema/) object.
   Useful to inspect whether types are defined in a schema.
 * `$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](https://graphql.org/learn/queries/#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.

```php
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:


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