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

[Joerg Baesner]

> 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
> > _______________________________________________
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> > hibernate-dev at lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/hibernate-dev
>
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>

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JOERG BAESNER

SENIOR SOFTWARE MAINTENANCE ENGINEER

Red Hat

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