[hibernate-issues] [Hibernate-JIRA] Created: (HHH-3771) Best pactice for equals implementation?

[Samppa Saarela (JIRA)]

Best pactice for equals implementation?
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                 Key: HHH-3771
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3771
             Project: Hibernate Core
          Issue Type: New Feature
          Components: core, documentation
            Reporter: Samppa Saarela


When domain model contains even one lazy reference to an object, default equals fails when it's compared to a) the actual implementation returned by Session.get/load or b) other proxies (at least of different supertype). Overriding equals on a class that uses surrogate id is not that simple. However there is a simple solution to this problem: 

In domain class, override equals like this:

public boolean equals(Object obj) {
  return this == getImplementation(obj);
}

public static Object getImplementation(Object obj) {
  if (obj instanceof HibernateProxy) {
    return ((HibernateProxy) obj).getHibernateLazyInitializer().getImplementation();
  } else {
    return obj; 
  }
}

This should result always in comparing object references of actual instances and thus preserve symmetry.

It's understandable that you don't wan to publish that kind of getImplementation utility e.g. in Hibernate, but maybe you could support this more directly by implementing 

Hibernate.equals(Object o1, Object o2) 

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