[hibernate-dev] HHH-12146 - subclass-specific caching

[Steve Ebersole]

And btw, this *has* to happen.  JPA requires it and the 2.2 TCK tests for
it.  So there is no "keep allowing caching at the root-level" option here


On Tue, Dec 12, 2017 at 12:44 PM Steve Ebersole <steve at hibernate.org> wrote:

> Its not any different than `#get( LegalEntity.class, key )` in the old
> config when key refers to a Person and Person is *not* in the cache simply
> because it has not been loaded/saved via this SF.
>
> On Tue, Dec 12, 2017 at 12:33 PM Sanne Grinovero <sanne at hibernate.org>
> wrote:
>
>> Conceptually it sounds useful but I'm wondering about this being safe
>> to do in various more tricky mapping scenarios.
>>
>> For example consider this case:
>>
>> @Inheritance(...)
>> @Cache(...)
>> @Cacheable(true)
>> class LegalEntity {
>>     ...
>> }
>>
>> @Cacheable(false)
>> class Person extends LegalEntity {
>>     ...
>> }
>>
>> @Cacheable(true)
>> class Company extends LegalEntity {
>>     ...
>> }
>>
>> [N.B. the parent class is no longer abstract]
>>
>> Now imagine we have to implement a polymorphic load: `load(key,
>> LegalEntity.class)`
>>
>> Would you be able to use the 2LC safely in all possible inheritance
>> mappings?
>>
>> I'm particularly curious about the possibility of a Person being
>> stored, but since we won't have data about the Person in the cache
>> we'd materialize the load as a LegalEntity.
>>
>> Incidentally while writing this example I realize that such a mapping
>> could trigger issues even with existing caching options.
>>
>> Thanks,
>> Sanne
>>
>>
>>
>> On 12 December 2017 at 14:49, Steve Ebersole <steve at hibernate.org> wrote:
>> > HHH-12146 is about being able to enable/disable caching at various
>> levels
>> > in an entity hierarchy.  E.g., given a hierarchy such as `Person` and
>> > `Company` both extending `LegalEntity`, this would allow users to say
>> that
>> > only `Company` should be cached but not `Person` nor any other
>> > `LegalEntity` subclass.
>> >
>> > The underlying approach here is to still define region and
>> access-strategy
>> > information per-hierarchy - users will simply be able to opt out of (or
>> > into) caching particular subclasses.  In my initial attempt I simply
>> > allowed both `@Cache` and `@Cacheable` to appear anywhere in the
>> > hierarchy.  However, allowing `@Cache` (as currently defined) implies
>> that
>> > users should be able to define different regions and/or access
>> strategies
>> > for various subclasses within the hierarchy.  Stepping back, I thought a
>> > better solution would be to continue to support `@Cache` only at the
>> root
>> > level and define this new feature in terms of `@Cacheable` at the
>> various
>> > levels.  This has a few implications that I wanted to discuss.
>> >
>> > The main thing is that this means that applications using just `@Cache`
>> to
>> > define caching would still only be able to declare caching for the
>> entire
>> > hierarchy.  But I think that is ok because that was the legacy behavior,
>> > and so nothing is really changing there.  If we find `@Cache` on the
>> root
>> > we'd assume an implicit `@Cacheable(true)`.  I think some examples will
>> > help explain...
>> >
>> >
>> > Current behavior
>> >
>> > @Inheritance(...)
>> > @Cache(...)
>> > abstract class LegalEntity {
>> >     ...
>> > }
>> >
>> > class Person extends LegalEntity {
>> >     ...
>> > }
>> >
>> > class Company extends LegalEntity {
>> >     ...
>> > }
>> >
>> > In the current behavior both  `@Cache` and `@Cacheable` are only valid
>> on
>> > the root as seen above.  Placing them on any subclass results in an
>> error.
>> > Note too that we could have used `@Cacheable` here instead of `@Cache`
>> in
>> > which case the default `@Cache` values would be applied.  It was also
>> legal
>> > to use both together.  In fact, a portable application would use
>> > `@Cacheable` with or without `@Cache`.
>> >
>> >
>> > Proposed behavior
>> >
>> > @Inheritance(...)
>> > @Cache(...)
>> > @Cacheable(false)
>> > abstract class LegalEntity {
>> >     ...
>> > }
>> >
>> > class Person extends LegalEntity {
>> >     ...
>> > }
>> >
>> > @Cacheable(true)
>> > class Company extends LegalEntity {
>> >     ...
>> > }
>> >
>> > Here we have the root disabling caching (assuming
>> > `SharedCacheMode.ENABLE_SELECTIVE`).  `Person` inherits that setting.
>> >  `Company` however overrides that to enable caching.  We still have
>> > `@Cache` attached to the root to define the specifics of caching
>> (region,
>> > access strategy).  But as noted earlier, we could have left off `@Cache`
>> > and accepted the defaults.
>> >
>> > I also propose that we continue to accept `@Cache` (without explicit
>> > `@Cacheable`) as implying `@Cacheable(true)` although `SharedCacheMode`
>> > plays a part in that too.
>> >
>> > Anyway, I wanted to make sure everyone agrees with this.
>> > _______________________________________________
>> > hibernate-dev mailing list
>> > hibernate-dev at lists.jboss.org
>> > https://lists.jboss.org/mailman/listinfo/hibernate-dev
>>
>