所有运行 GraphQL 的服务器必须至少有一个 @Query() 才能被视为有效的 GraphQL 服务器.没有它，apollo-server 包将抛出异常，服务器将无法启动.这可以很简单

All servers running with GraphQL must have at least one @Query() to be considered a valid GraphQL server. Without it, the apollo-server package will throw an exception and the server will fail to start. This can be as simple as

@Resolver()
export class FooResolver {

  @Query(() => String)
  sayHello(): string {
    return 'Hello World!';
  }
}