refs #9548
- do not forward `tag.parent` to the model layer
- the model layer should only know `tag.parent_id`
- and the API should only expose `tag.parent` (this is an API feature)
- currently Ghost has a mixture of using `toJSON` and the API validation layer for this
- we just continue with this for now (no time to fix this)
- disallow sending nested-nested relations
- unsupported
- see comment for more information
- this can cause problems with calling `hasChanged` on relations
- add unit tests
bda76acba6