[hibernate-dev] Null vs "empty" embeddable values

[Steve Ebersole]

No I mean checking on start up similar to what we do for composite id
classes.  So basically if this setting is enabled (treat all nulls == empty
composite) make sure that the composite overrides equals/hashCode.



On Wed, Jul 26, 2017 at 6:08 PM Gail Badner <gbadner at redhat.com> wrote:

> Hi Steve,
>
> IIUC, you are suggesting:
>
> if ( !emptyValue.equals( null ) || emptyValue.hashCode() != 0 ) {
>      LOG.warn( ... );
> }
>
> I originally mentioned this issue with respect to Collection methods
> called on collections of embeddable values, but it could apply to
> empty/null embeddables in singular attributes as well.
>
> This warning would apply regardless of the setting for
> hibernate.create_empty_composites.enabled, since an application itself
> could set null or empty embeddable values.
>
> After thinking about this more, I suspect that such a warning would get
> logged for many (most?) embedded values.
>
> There is also a complication that Hibernate will inject the parent into an
> empty value if @Parent is mapped on a property in the embeddable. That
> (non-empty) parent could affect what gets returned by #equals and/or
> #hashCode.
>
> I've been trying to figure out a good place for checking to minimize the
> warnings.
>
> Here are some options:
>
> 1) Check when the owner PersistentClass is being validated by
> MetadataImpl#validate.
>
> Component#validate could be added to override SimpleValue#validate. If
> the check fails, a warning will logged in each context where the embeddable
> is used.
>
> Unfortunately, if @Parent is used in the embeddable class, there would be
> no way to check if parent attribute affects #equals or #hashCode since
> there is (obviously) no parent when validating the PersistentClass.
>
> 2) Check after Hibernate instantiates an empty value when resolving a null
> value with hibernate.create_empty_composites.enabled=true  by
> ComponentType#resolve(Object value, SharedSessionContractImplementor
> session, Object owner).
>
> I believe the parent would be provided to the method, so it would be
> available to check. I'd have to check to be sure though.
>
> If the parent contributes to the return values of #equals or #hashCode,
> there are other considerations to take into account.
>
> At the time ComponentType#resolve is called, the parent may not be
> completely resolved; it may not be valid to call those methods when the
> component is being resolved.
>
> Calling #hashCode and #equals on the parent each time Hibernate
> instantiates an empty value when resolving a null value (with
> hibernate.create_empty_composites.enabled=true) could hurt performance.
>
> If the check fails, lots of warnings could be logged.
>
> My opinion...
>
> After thinking about this as I'm writing this, I think 1) makes sense if
> there is no parent; 2) has too many problems to be workable.
>
> Any other ideas about how to deal with this?
>
> I don't think there is anything in the user guide that discusses how
> Hibernate treats null and empty embeddables as equivalent. There have been
> issues reported periodically related to collections. The most recent
> is HHH-11723. I think it would be worthwhile documenting this information
> in the user guide.
>
> Comments?
>
> Thanks,
> Gail
>
> On Wed, Jul 26, 2017 at 6:01 AM, Steve Ebersole <steve at hibernate.org>
> wrote:
>
>> "Requirement" - no.  I think a warning in this case is perfectly fine.
>>
>> As for JPA, it says nothing about embeddables and nulls.
>>
>> On Sun, Jul 23, 2017 at 6:49 PM Gail Badner <gbadner at redhat.com> wrote:
>>
>>> As of HHH-7610, Hibernate is supposed to treat null and empty embeddable
>>> values as equivalent.
>>>
>>> Should we add a requirement that an embeddable class #equals and
>>> #hashCode
>>> methods also treats null and "empty" values as equivalent?
>>>
>>> That would mean that #hashCode returned for all empty embeddables should
>>> be
>>> 0, and embeddableValue.equals( null ) should return true for all empty
>>> embeddableValue.
>>>
>>> BTW, I've already pushed a fix for HHH-11881 so that nulls are not
>>> persisted for Set elements (they already were not persisted for bags,
>>> idmaps, lists, or maps). I'm holding off on fixing HHH-11883, which would
>>> no longer persist empty embeddable values and would ignore embeddables
>>> with
>>> all null columns when initializing collections.
>>>
>>> I don't think JPA has any such requirement, and I'm hesitant to enforce
>>> something that may be at odds with JPA.
>>>
>>> Comments or opinions?
>>>
>>> Thanks,
>>> Gail
>>> _______________________________________________
>>> hibernate-dev mailing list
>>> hibernate-dev at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>>>
>>
>