Spring Data Repository - composite key & don't need to save entity - jpa

Question

I'm working with a third party database that is read-only. I have the following Spring Data repository:
public interface FolderRepository extends Repository<Folder, Integer> {
#Query(value = "SELECT f.folderId, a.fileId, a.fileName, " //selecting other columns in my app
+ "FROM User.functionSys(:binData) f "
+ "LEFT JOIN User.vFile a "
+ "ON f.fileId = a.fileId "
+ "group by f.folderId, a.fileId, a.fileName",
nativeQuery = true)
List<Folder> getFolders(#Param("binData") byte[] binData);
}
Folder id and file id form an unique key. So, my folder entity looks like this:
#Entity
#Data
public class Folder implements Serializable {
private static final long serialVersionUID = 1L;
#EmbeddedId
private FolderFileKey id;
private String fileName;
// several other fields in my app
}
#Embeddable
#Data
class FolderFileKey implements Serializable {
private static final long serialVersionUID = 2L;
private Integer folderId;
private Integer fileId;
}
The problem is that I really want a list of File objects where each File object contains a list of Folders (the same file id may be in several different folders):
#Data
public class FileDto {
private Integer fileId;
private String fileName;
private List<Folder> folders;
}
#Data
public class FolderDto {
private Integer folderId;
private String folderName;
}
I know that I could write a service to transform a Folder entity into the FileDto and FolderDto but is there a way to use Spring Data projections or rewrite the entities to achieve the structure wanted in the Dtos?
Update
User.functionSys(:binData) is a table-valued function (so it returns a table).