Including resources not directly connected

[SafaAlfulaij]

Sometimes I'd like to include a resource (notification for example) to a response without it being linked to any of the resource, or the linkage wil be hard.
I mentioned "notification" because it's the easiest, and I shouldn't treat it as map since it can diverge a lot.

[sliverc]

REST and JSON:API does not support something like this - if you have such use case you should consider using GraphQL.

This said if you have a simple case where one resource should always return the same non-related resources you could use SerializerMethodResourceRelatedField.