Projections require Entity Id field to not throw exception while instantiating #2088
Description
Issue Description
When creating interface projections that only expose specific fields (closed projections), omitting the entity's @Id field can result in runtime errors during proxy creation, even when the projected fields contain valid non-null data.
Entity
@Data
@Builder
@Table("file")
public class File {
@Id
private Long id;
private String fileId;
private Long uploaderId;
private LocalDateTime uploadDate;
private String fullName;
@Builder.Default
@MappedCollection(idColumn = "file_id")
private Set<Document> documents = new HashSet<>();
}Projection
public interface FilePreview {
String getFileId();
LocalDateTime getUploadDate();
}Repository
public interface FileRepository extends CrudRepository<File, Long> {
List<FilePreview> findBy();
}When invoking findBy an java.lang.IllegalStateException is thrown with message Identifier value must not be null at this point.
Modifying the projection to
public interface FilePreview {
Long id;
String getFileId();
LocalDateTime getUploadDate();
}results in the method not throwing exception.
The documentation does not mention anywhere this as an intended behaviour and it's not clear why would it be needed.