spring-data-rest return multiple projections at once (compose projections) - spring-data-rest

Question

Is there possibility to compose multiple projections? Is it best approach for my use case?
I have these projections for CarInBazar class for example:
SimpleCarInList
WidgetForHotSale
NumberOfItemViews
FullCarData
CarMainImage
CarMainImageIconSize
CarAdditionalImages
And frontend is now making some UI page, which requires some of these projections.
Should I do:
frontend will do multiple requests for same resource with different projections
Implement Projection for each screen of frontend (duplicating things like NumberOfItemViews calculation,...)
Use inheritance and make specific projections utilizing extends keyword. i.e.:
#Projection(name = "screen-dashboardHome", types = {CarInBazar.class})
public interface DashboardHomeProjectionForCarInBazar extends SimpleCarInList,
WidgetForHotSale, CarMainImageIconSize {
}
Is there any possibility to request more projections at once? It could be than rendered in UI using provided profiles perhaps.
EDIT: as requested, providing projection definition example:
import org.springframework.data.rest.core.config.Projection;
import java.awt.*;
import java.util.Date;
#Projection(name = "CarMainImage", types = {CarInBazar.class})
public interface CarMainImage {
Date getLastUpdateDate();
Image getMainImage();
default String getMainImageAdditionalInformation() {
final var updated = this.getLastUpdateDate().getTime();
final var created = this.getCreatedAtDate().getTime();
if (created >= (updated - 10 minutes)) {
return "some business logic on not published fields";
} else {
return "could happen not only in spel";
}
}
}
Many projections does not contain any business logic and are only filtering fields.

Answer 1

Using multiple projections seems to not be supported (or widely supported or easy). Using suggestion from #Aivaras comment I have used this approach:
Repository code with custom JPQL query:
#Repository
#RepositoryRestResource
#Transactional(readOnly = true)
public interface SomeRepository extends PagingAndSortingRepository<Some, Long> {
Page<Some> findByNameContaining(String namePart, Pageable pageable);
#Query("select new sk.qpp.documents.projections.SomeCustomViewByQuery(s.name, s.startDate, s.endDate, s.goLiveDate, 42) from Some s where s.id = :id")
Optional<SomeCustomViewByQuery> getByIdProjectedForSpecialScreen(Long id);
}
And class SomeCustomViewByQuery is just simple DTO like thing. Using lombok it can look like:
#Value
public class SomeCustomViewByQuery {
private String name;
private Date startDate;
private Date endDate;
private Date goLiveDate;
// TODO make SomeHealth to be enum and specific logic behind it.
String getSomeHealth() {
final var start = this.getStartDate().getTime();
final var end = this.getEndDate().getTime();
final var goLive = this.getGoLiveDate().getTime();
final var now = System.currentTimeMillis();
if (now < start) {
return "not started yet";
} else {
if (now < end) {
return "work in progress";
} else {
if (now < goLive) {
return "passed end, but before goLive";
} else {
return "something after goLive time";
}
}
}
}
private int unicornsCount;
}
This way, I can make hand-crafted query (JQPL) and also create custom DTO instance. It is handy, where I need to do some joins to other tables with aggregation (count, avg, max, min, ...) and other things, which are better done on database side.