Better support for composite types [DATAREST-786]

Stefan Fussenegger opened DATAREST-786 and commented

The current implementation is a bit clunky when dealing with composition objects, i.e. 1:n relationships. Most notably it should be possible to POST composition objects directly to the resource (e.g. /building/1/rooms) rather than having to POST the object and later link it.

The case of PUT to /building/1/rooms/301 is a bit trickier, but since GET and DELETE actually work already it should probably be supported too. The possibility of allowing duplicate room IDs in different buildings would be an interesting one though - as it probably is to be expected.

The current implementation of RepositoryPropertyReferenceController.createPropertyReference(..) should be relatively safe to extend in this way. However, backward compatibility would be tricky since this method is already accepting application/json actually expecting application/hal+json (and there only the _links, _embedded is silently ignored). Additionally, this mapping is prohibiting the addition of a custom controller mapping

Affects: 2.4.4 (Gosling SR4)