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

[Sanne Grinovero]

We discussed this further in chat. For the sake of others reading, the
summary: I got confused about the risks of having multiple cache
regions for a single hierarchy; the proposal is *not* to have multiple
regions yet be able to exclude specific types from the (shared) region
of a type hierarchy.

Sounds great.

On 12 December 2017 at 18:45, Steve Ebersole <steve at hibernate.org> wrote:
> 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