@NotNull on subclass getter affects parent class table

Question

I have a question related to javax.validation.constraints.NotNull annotation. In my project i do have classes tree like following :

@Inheritance(strategy = InheritanceType.JOINED)
class Ssss {
    @ManyToOne
    private Xxxx x;
    public Xxxx getXxxx() {
       return x;
    }
}

@Inheritance(strategy = InheritanceType.JOINED)
class Yyyy extends Ssss {
    @Override
    //some not important annotations
    public Xxxx getXxxx() {
        return super.getXxxx();
    }        
}

@Inheritance(strategy = InheritanceType.JOINED)
class Zzzz extends Ssss {
    @Override
    //some not important annotations
    @NotNull
    public Xxxx getXxxx() {
        return super.getXxxx();
    }
}

This three classes are stored in database as three tables. For schema creation i'm using Hibernate:

hibernate.hbm2ddl.auto=create

Is it an expected behavior that Hibernate adds NOT NULL on xxxx_object_id field stored in table generated for super class ssss like following:??

I could not find any relevant information about how hibernate treats @NotNull on inherited getters.

Can anyone help me on this issue?
Best Regards.
Michal

Answer 1

Yes. Hibernate has constraints which it keeps checking in case of conflicts.
Here is an example:

@Inheritance(strategy = InheritanceType.JOINED)
class Ssss {

   @ManyToOne
   private Xxxx x;
   public Xxxx getXxxx() {
      return x;
   }
}

If it was this much, then hibernate has no Conflict as it makes x of type Xxxx as null
But here is the issue, in this code:

@Inheritance(strategy = InheritanceType.JOINED)
class Zzzz extends Ssss {
   @Override
   //some not important annotations
   @NotNull
   public Xxxx getXxxx() {
       return super.getXxxx();
   }
}

Here Hibernate via @NotNull annotation is told to make the x type of Xxxx as @NotNull
In the above two cases, there is a conflict, for Ssss it can be Null and Zzzz it cannot be null. To infer that and resolve the conflict, Hibernate makes Xxxx type variable of Ssss as NotNull as well.