Preserve object identity in parent-child relations of a Hibernate model

Question

I have the following scenario and could not find any solution for this so far.

Imagine the following Hibernate model consisting of 3 different types with one-to-many relations:

public class A {
  
  @Transient
  private String someRuntimeData;

  @OneToMany
  private Set<B> collA;

  @OneToMany 
  private Set<C> collB;
}


public class B {
  @ManyToOne
  private A parent;
}


public class C {
  @ManyToOne
  private A parent;
}

Imagine that the database contains many B'c and C's that may or may not have a parent relation to A yet. I need to create an in-memory cache that contains all B's and all C's, and unfortunately there is a lot of transient data in different places involved, which requires me to suppress caching multiple instances of the same parent object A.

class SomeClass {
     @Transactional
     protected void init() {
       bList = repoB.readAll();
       cList = repoC.readAll();
     }
  }

The problem is that I don't know how or if it is even possible to tell JPA/Hibernate to retain and reuse an object instance (with its identity) of previously loaded entities in the following way:

Load the full collection of B's with their optional parents of A, then load the full collection of C's, where any transitively loaded instance of A (through B) is reused. Where appropriate, both B and C instances then point to the same in-memory object.

I would be very thankful if anyone could explain on how to realize this with out-of-box features of JPA/Hibernate before I swallow the bitter pill and and remap everything by hand.

Thank you in advance!

Basically, that's what happens within in a single transaction. — Mihe, Oct 10 '22 at 17:52
That's what I thought, and I annotated the method containing the JPA readAll() calls to both B's and C's, yet the same parents had a different object identities. Would Spring tell me with an error or warning that the transactional context is in fact not applied to the method, or just fail silently? — godsim, Oct 11 '22 at 07:22
You annotated readAll() or the class containing this method with `@Transactional`? — Mihe, Oct 11 '22 at 09:23
@Mihe I added an additional code snippet regrding the "@Transactional" part. — godsim, Oct 12 '22 at 07:07
You coud try to debug this, e. g. [this answer](https://stackoverflow.com/a/69894165/19657183) might be helpful. — Mihe, Oct 12 '22 at 09:54
@Mihe Although my problem had another cause, this was very helpful in understanding when Spring opens and closes certain transactions in my code. Thank you very much! — godsim, Oct 12 '22 at 13:20

score 1 · Answer 1 · answered Oct 12 '22 at 13:32

It was not obvious from the provided code snippets what the problem could have been in this scenario.

For full disclosure, the init() method was called via self-invocation from the classes constructor:

@Component
class SomeClass {
    
    public SomeClass() {
      init();
    }

    @Transactional
    protected void init() {
      bList = repoB.readAll();
      cList = repoC.readAll();
    }
}

Since I did not configure any aspect-weaving for load- or runtime, the compiler created a default Spring Proxy object for SomeClass. Therefore any proxy logic is fully circumvented when self-invocation is in play. In result, the only transactions opened where the default, dedicated ones for each read operations, and the shared parent objects where redundantly loaded.

Preserve object identity in parent-child relations of a Hibernate model

1 Answers1