[hibernate-dev] Composite IDs with a null property/field

[Emmanuel Bernard]

My answer is that if the code change looks too impactful I'm fine with 
no supporting such scenario.

On 11 Dec 2019, at 11:24, Joerg Baesner wrote:

> > ...  I suppose some means it as default.
>
> Yes, exactly.
>
> Your reply doesn't answer the question if Hibernate shouldn't support 
> this
> scenario. Anyhow, what Gail already wrote is that Hibernate returns 
> null
> for the entity result, leading to a null value in a returned 
> ResultList,
> which seem to be wrong...
>
> On Wed, Dec 11, 2019 at 11:16 AM Emmanuel Bernard 
> <emmanuel at hibernate.org>
> wrote:
>
>> We have been trying to keep a balance of maintainable code base for
>> Hibernate vs legacy/counter intuitive/plain wrong DB designs. The 
>> answer is
>> never clear cut. In your case I'm not sure what a bundle + key means 
>> if it
>> does not have a locale - I suppose some means it as default.
>>
>> On 11 Dec 2019, at 10:49, Joerg Baesner wrote:
>>
>>> I think in the past we argued the same for attributes of a composite 
>>> id,
>>> like you said, if one of the element can be nul, why is it in the id
>>> property in the first place.
>>
>> As an example you might Imagine someone wants to put 
>> internationalization
>> properties into a database and having a table structure like this 
>> (this
>> might be an old legacy application that doesn't have a PK column):
>>
>> BUNDLE_NAME (not nullable)
>> KEY (not nullable)
>> LOCALE (nullable)
>> VALUE (not nullable)
>>
>> The first 3 (BUNDLE_NAME, KEY, LOCALE) are the CompositeKey and 
>> there's a
>> unique constraint on the database on these columns.
>>
>> It is fine to have the LOCALE as <null>, as in this case the systems
>> default locale would be used, but for each BUNDLE_NAME/KEY 
>> combination you
>> could only have a single composite key with a <null> LOCALE.
>>
>> Hibernate should be (must be?) able to handle this scenario, what do 
>> you
>> think?
>>
>> Joerg
>>
>> On Wed, Dec 11, 2019 at 10:18 AM Emmanuel Bernard 
>> <emmanuel at hibernate.org>
>> wrote:
>>
>>> Just talking about simple id, even if we allow the column to be 
>>> nullable
>>> (if the DB even allows that), I don't think Hibernate allows null to 
>>> be
>>> a valid id value. Because null means I don't know or not applicable.
>>> I think in the past we argued the same for attributes of a composite 
>>> id,
>>> like you said, if one of the element can be nul, why is it in the id
>>> property in the first place.
>>>
>>> As for whether there is a strong implementation detail reason to not
>>> allow it, I don't know but I assume the null checking assuming "not 
>>> an
>>> id" is pretty much all over the place.
>>>
>>> Emmanuel
>>>
>>> On 11 Dec 2019, at 3:37, Gail Badner wrote:
>>>
>>>> Currently, there is no way to load an entity that exists in the
>>>> database
>>>> with a composite ID, if one of the composite ID columns is null.
>>>>
>>>> This behavior is due to this code in ComponentType#hydrate:
>>>>
>>> https://github.com/hibernate/hibernate-orm/blob/master/hibernate-core/src/main/java/org/hibernate/type/ComponentType.java#L671-L675
>>>>
>>>> Basically, if any field/property in a composite ID is null, 
>>>> Hibernate
>>>> assumes the entire ID is null. An entity cannot have a null ID, so 
>>>> it
>>>> returns null for the entity result.
>>>>
>>>> I believe that Hibernate does allow a primary key column to be
>>>> nullable.
>>>>
>>>> TBH, it seems strange to have a property in a composite ID that can 
>>>> be
>>>> null. If it can be null, it seems that the property could be 
>>>> removed
>>>> from
>>>> the composite key.
>>>>
>>>> I don't see anything in the spec about a requirement that all
>>>> composite ID
>>>> fields/properties must be non-null. Am I missing something?
>>>>
>>>> The code I referenced above is 13 years old. Does anyone have 
>>>> insight
>>>> into
>>>> why Hibernate does this?
>>>>
>>>> Thanks,
>>>> Gail
>>>> _______________________________________________
>>>> hibernate-dev mailing list
>>>> hibernate-dev at lists.jboss.org
>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>>>
>>> _______________________________________________
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>>> hibernate-dev at lists.jboss.org
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>>>
>>>
>>
>> --
>>
>> JOERG BAESNER
>>
>> SENIOR SOFTWARE MAINTENANCE ENGINEER
>>
>> Red Hat
>>
>> <https://www.redhat.com/>
>>
>> jbaesner at redhat.com    T: +49-211-95439691
>> <https://red.ht/sig>
>> TRIED. TESTED. TRUSTED. <https://redhat.com/trusted>
>>
>>
>
> -- 
>
> JOERG BAESNER
>
> SENIOR SOFTWARE MAINTENANCE ENGINEER
>
> Red Hat
>
> <https://www.redhat.com/>
>
> jbaesner at redhat.com    T: +49-211-95439691
> <https://red.ht/sig>
> TRIED. TESTED. TRUSTED. <https://redhat.com/trusted>