spring - Traversing a collection causes SQL update

Question

I am struggling with this..

Whenever I traverse a collection inside a transaction it will trigger an SQL update for one of its field.

@Entity
class A {
    @ManyToOne
    @JoinColumn(name = "b1_id")
    private B b1;

    @ManyToOne
    @JoinColumn(name = "b2_id")
    private B b2;
}

Unidirectional so B knows nothing about A.

    @org.springframework.transaction.annotation.Transactional  //1. do nothing
    private void doSomething(){     
     List<A> aEntities = aRepository.findAll();
    }


   @org.springframework.transaction.annotation.Transactional //2.traversing the list
   private void doSomething(){     
         List<A> aEntities = aRepository.findAll();
         for (A a: aEntities){
          //dont do anything
         } 
   }

   private void doSomething(){    // 3.no transaction
    List<A> aEntities = aRepository.findAll();
         for (A a: aEntities){
          //dont do anything
         } 
   }

SQL log shows:

1. only SELECT is generated
2. UPDATE for b1  (but not for b2) !!!!!
3. only SELECT is generated

And on the top of that 2 UPDATE will be run for b1. If I turn on JPA versioning I can see that b1's version is incremented by 2, b2 left untouched.(If I remove b2, the same update will be launched for b1)

This drives my nuts....

The class B is unimportant imo because for the other instance of it no update will be generated. And I have several other classes with manytoany assocciations but never encountered such an issue. This situation comes up only for b1 in entity A.

Answer 1

等待大神答复