JaversException ENTITY_INSTANCE_WITH_NULL_ID for ignored id - javers

Question

Using javers 5.11.2 I get the following exception although the id is set to be ignored. Why is that?
JaversException ENTITY_INSTANCE_WITH_NULL_ID: Found Entity instance 'my.package.javers.Leaf' with null Id-property 'id'
Update: I learned that
JaVers matches only objects with the same GlobalId
The id is specified using javax.persistence.Id. However, with each ORM it is possible to have an entity with a collection, then add a new element without id to that entity and then save it (CascadeType.Persist).
Is there any way to compare objects with javers in such a case?
Example (used lombok for boiler plate code).
The leaf:
#AllArgsConstructor
#NoArgsConstructor
#Builder
#Data
#Entity
public class Leaf {
#DiffIgnore <============ id is ignored
#Id
private Long id;
private String color;
}
The tree:
#Builder
#Data
#Entity
public class Tree {
#Id
private Long id;
private String name;
#OneToMany
private Set<Leaf> leafs;
}
Test adds a leaf to the oakSecond without an id set. The diff cannot be made. An Exception is thrown.
#Test
public void testCompare_AddLeafToTree() {
Leaf leaf = Leaf.builder().id(1L).color("11").build();
Set<Leaf> leafsOfOakFirst = new HashSet<>();
leafsOfOakFirst.add(leaf);
Tree oakFirst = Tree.builder().id(1L).name("oakFirst").build();
oakFirst.setLeafs(leafsOfOakFirst);
Set<Leaf> leafsOfOakSecond = new HashSet<>();
leafsOfOakSecond.add(leaf);
leafsOfOakSecond.add(Leaf.builder().color("12").build());
Tree oakSecond = Tree.builder().id(1L).name("oakFirst").build();
oakSecond.setLeafs(leafsOfOakSecond);
Javers javers = JaversBuilder.javers().build();
Changes changes = javers.compare(oakFirst, oakSecond).getChanges();
assertThat(changes).isNotEmpty();
}
Same with the following definition of the Javers instance:
EntityDefinition leafEntityDefinition = EntityDefinitionBuilder.entityDefinition(Leaf.class).withIgnoredProperties("id").build();
Javers javers = JaversBuilder.javers().registerEntity(leafEntityDefinition).build();

Answer 1

You can't pass an Entity to Javers with null Id because it would be non-identifiable. If you use Hibernate to generate your Ids, make sure that you pass your object to javers.commit() after hibernate are done with its job. That's how the #JaversSpringDataAuditable aspect works.
Alternatively, you can model those objects with unstable IDs as Value Object in Javers.