Response when updating relationship of resource not conform spec

[maurei]

This issue is analogous to #577 but for relationships instead of attributes.

200 OK
If a server accepts an update but also changes the targeted relationship(s) in other ways than those specified by the request, it MUST return a 200 OK response. The response document MUST include a representation of the updated relationship(s).

A server MUST return a 200 OK status code if an update is successful, the client’s current data remain up to date, and the server responds only with top-level meta data. In this case the server MUST NOT include a representation of the updated relationship(s).

the part in bold is currently not properly implemented.

The associated repository method does not return anything:

public interface IEntityWriteRepository<TEntity, in TId>
    where TEntity : class, IIdentifiable<TId>
{
  ....
  Task UpdateRelationshipsAsync(object parent, RelationshipAttribute relationship, IEnumerable<string> relationshipIds);
  ....
}

This is fine for the default implementation. But if, as in #577, a developer has business logic that affects the relationships in a way different than as specified by the request, a response must include a representation of the updated relationships

[bart-degreed]

If a server accepts an update but also changes the targeted relationship(s) in other ways than those specified by the request

I cannot think of a scenario in which this applies. An example would be helpful.

[maurei]

We have decided to hold off implementing this part of the spec because we are not sure what any use-case for this would be. For a more detailed consideration, please check out json-api/json-api#1524