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

[Samppa Saarela (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3771?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=32348#action_32348 ] 

Samppa Saarela commented on HHH-3771:
-------------------------------------

I accidentaly submitted that a bit too early... I also meant to say:

* Is there some error or hidden pitfall to this approach of overriding equals and using == on an actual implementation returned by the LazyInitializer? 

* Adding an equals(Object, Object) -utility method to Hibernate with this kind of semantics would make identity handling in Hibernate more safe for classes which cannot easily implement natural key.

> Best pactice for equals implementation?
> ---------------------------------------
>
>                 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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