Fetch collection of resource that do have relationship established with another resource

1

In a one-to-many relationship.
When one resource can be associated to 0 or multiple other resource then if I have a requirement to fetch collection of resource that does not have the association established, then how would i do that?

2

It’s a little unclear what you’re referring to, but if you’re talking about fetching a relationship. You’d return an empty array. See JSON:API — Latest Specification (v1.1)

3

If you want to filter a collection to only request those, which have an empty relationship, you should use filter query parameter as with any other filtering.

The JSON:API specification os agnostic on your filter strategy. You are free to chose what ever syntax you prefer to encode that filter criteria as a query parameter.