[hibernate-dev] Entity implementation of equals()

[Jan-Willem Gmelig Meyling]

I tend to use this.getClass().isInstance(o) and this.getClass().cast(o) which works even in a mapped super class on most occasions. (Assuming that the proxy delegates equals to a concrete target).


Jan-Willem


> Op 27 aug. 2019 om 22:29 heeft Steve Ebersole <steve at hibernate.org> het volgende geschreven:
> 
> Generally speaking an `#equals` method would not allow subclasses to
> match.  For entity mappings specifically I this it is generally considered
> kosher to allow subclass matching in `#equals`.  Interestingly, when
> generating `#equals` overrides through IntelliJ it even asks specifically
> whether subclasses should be allowed to match.  In fact it mentions (or
> used to mention) Hibernate specifically wrt proxies in the dialog.
> 
> And it's actually required (as you found) if you want to use Hibernate's
> proxy-based lazy loading.
> 
> However, this is a case with a MappedSuperclass and specifically a
> MappedSupperclass that is I guess shared amongst multiple root entities.
> So here the allowance of subclasses is not really feasible and relying on
> any kind of equality checking defined on the MappedSuperclass is not going
> to work
> 
>> On Tue, Aug 27, 2019 at 6:49 PM Gail Badner <gbadner at redhat.com> wrote:
>> 
>> Hi,
>> 
>> I'm looking into the impact of HHH-13590.
>> 
>> In the test for HHH-13590, I see that the mapped superclass entity defines
>> equals() as:
>> 
>> @Override
>> public boolean equals(Object o) {
>>   if (this == o) return true;
>>   if (o == null || getClass() != o.getClass()) return false;
>> 
>>   ...
>> 
>> }
>> 
>> Due to the bug:
>> * this is a Project instance;
>> * o is a HibernateProxy with target == this.
>> 
>> Because the getClass() != o.getClass(), false is returned, and that
>> ultimately causes the test to fail.
>> 
>> The fix for HHH-13590 results in comparing a Project instance with itself
>> (not the proxy).
>> 
>> I see that the documentation has a similar implementation of equals() in
>> "Example 111. Natural Id equals/hashCode" of [1].
>> 
>> In general, is it OK for equals() to require both instances to be of the
>> same class?
>> 
>> Thanks,
>> Gail
>> 
>> [1]
>> 
>> https://docs.jboss.org/hibernate/orm/5.4/userguide/html_single/Hibernate_User_Guide.html#mapping-model-pojo-equalshashcode
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