Add support for query methods returning a projection [DATAREST-841]

Oliver Drotbohm opened DATAREST-841 and commented

Currently Spring Data REST does not support returning projections from query methods directly. The feature has been introduced for Spring Data JPA and MongoDB in the Hopper release train and it would be cool to get this working in Spring Data REST, too.

Currently the problem is that PersistentEntityResourceAssembler and a couple of downstream components try to lookup a PersistentEntity for the returned instance's type which fails due to the proxy type being used and not the underlying target class. Even if that's fixed, the question is how we can make sure to be able to create self links properly as the identifier property is not guaranteed to be exposed by the proxy and contrary to the projection mechanism applied by Spring Data REST the proxy might not be backed by the actual domain object.

For DTOs used, we might even run into problems in the MappingContext as e.g. JPA currently only considers managed types a PersistentEntity

Issue Links:

• DATAREST-1257 Spring Data Projection doesn't work when using with Page
  ("is duplicated by")
• DATAREST-1054 Exposing projections from query methods on the repository level
  ("is duplicated by")
• DATAJPA-885 No aliases found in result tuple

8 votes, 10 watchers