Re: [hibernate-dev] HHH-12146 - subclass-specific caching
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(a)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.
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