Subscriptions
In GraphQLite, subscriptions are created like queries or mutations.
To create a subscription, you must annotate a method in a controller with the #[Subscription] attribute.
For instance:
namespace App\Controller;
use TheCodingMachine\GraphQLite\Annotations\Mutation;
class ProductController
{
#[Subscription(outputType: 'Product')]
public function productAdded(?ID $categoryId = null): void
{
// Some code that sets up any connections, stores the subscription details, etc.
}
}
As you will notice in the above example, we're returning void. In general, this is probably the
correct return type.
You could, however, type the Product as the return type of the method, instead
of using the outputType argument on the #[Subscription] attribute. This means you
would have to return an instance of Product from the method though. One exception here, is if
you intend to use PHP for your long-running streaming process, you could block the process inside
the controller and basically never return anything from the method, just terminating the
connection/stream when it breaks, or when the client disconnects.
Most implementations will want to offload the actual real-time streaming connection to a better suited
technology, like SSE (server-sent events), WebSockets, etc. GraphQLite does not make any assumptions
here. Therefore, it's most practical to return void from the controller method. Since GraphQL
is a strictly typed spec, we cannot return anything other than the defined outputType from the request.
That would be a violation of the GraphQL specification. Returning void, which is translated to null
in the GraphQL response body, allows for us to complete the request and terminate the PHP process.
We recommend using response headers to pass back any necessary information realted to the subscription. This might be a subscription ID, a streaming server URL to connect to, or whatever you need to pass back to the client.