Sometimes you want to know what fields are queried before you'll query your db etc. It often reduces number of db queries etc.
To do that, we can use custom @Inject argument decorator that will resolve to list of needed subfields. Such information can be passed to any orm etc.
I've based this decorator on great lib: https://github.com/jakepusateri/graphql-list-fields that is able to get string[] of needed fields out of info graphql variable.