What about nested objects like “formats”?
Well, that depends. A field can take form of a nested object in the API response for multiple reasons:
- it’s a relation
- it’s a component (which is in fact just a special case of relation)
- it’s a media field (again a special case of relation)
- it’s a Dynamic zone
- it’s a JSON field
The populate and fields parameters, to my knowledge, are supported only for the basic relation fields i.e. relations, components and media.
The format field of the plugin::upload.file content-type is a JSON field and hence cannot be fetched partially.
You could work around this by implementing a custom controller that strips out everything you don’t need from the response.