org.hibernate.id.IdentifierGenerationException：试图从空一对一属性（hibernate+postgres）分配id

Question

I'm using hibernate 5.3.11 with SpringDataJpa and PostgreSQL and I get "org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property [packagename.ClassB.classA]" when trying to update a complex entity ClassC.

• ClassC is @OneToMany with ClassA
• ClassA is @OneToOne with ClassB.
• All entities have links to each other before calling update method.
• ClassC is a parent entity and cascades to ClassA, which cascades to ClassB.
• The issue seems to be related only to A<->B relationship.
• show-sql tells me that ClassA persists fine, but seems like for some reason it looses link to ClassB somewhere in hibernate.
• Persisting entity for the first time works fine. The error only comes on update. And I don't even update existing entities of ClassB and ClassA, I replace them with new ones.

Relationship:

ClassB in SQL :

ClassA in SQL :

Java entities:

@Data
@Entity
@EqualsAndHashCode(exclude = {"classA"})
public class ClassA {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    @ManyToOne
    @JoinColumn(name = "classC_id")
    private ClassC classC;
    
    @OneToOne(mappedBy = "classA", cascade = CascadeType.ALL)
    private ClassB classB;
}
    
@Data
@Entity
public class ClassB {
    
    @Id
    private Long id;
    
    @OneToOne
    @JoinColumn(name = "id")
    @MapsId
    private ClassA classA;
}

Answer 1

Short Answer: I used SpringBoot ver.2.1.8. Updating to 2.2.1 helped. Long answer here Post-upgrade, @MapsId is throwing an error when saving an existing entity, but otherwise works fine