Allow the Definition of Projections as Mongo Aggregations or SQLViews [DATAREST-1122]

Gregor Frey opened DATAREST-1122 and commented

I would like to have the possibilities to define Spring Data Rest projections by Mongo Aggregations, and this same feature could probably also be extended to SQLViews. The goal is to do filtering, joining, projecting data in the database to reduce the roundtrips to the DB and also reduce the amount of data transferred. Also I'd like to get it integrated with the Spring Data Rest Hateoas restification, as any other projection.
The Spring Data Mongo module provides also a concept of projections (which is, as far as I can see, unrelated to the Spring Data Rest concept), but it cannot be used with mongo aggregations, because they can not be defined as repository finders, and they are not integrated with the repository restification of Spring Data Rest.
I think this would be a cool feature that improves the performance and also reduces the momory consumption of a mongo app a lot.

Affects: 3.0 RC2 (Kay)