13.3. Entity inheritance and second-level cache mapping

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When using inheritance, the JPA `@Cacheable` and the Hibernate-specific `@Cache` annotations should be declared at the root-entity level only.
That being said, it is not possible to customize the base class `@Cacheable` or `@Cache` definition in subclasses.

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<div class="paragraph">

Although the JPA 2.1 specification says that the `@Cacheable` annotation could be overwritten by a subclass:

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> <div class="paragraph">

The value of the `Cacheable` annotation is inherited by subclasses; it can be
overridden by specifying `Cacheable` on a subclass.

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<div class="attribution">
&#8212; Section 11.1.7 of the JPA 2.1 Specification
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<div class="paragraph">

Hibernate requires that a given entity hierarchy share the same caching semantics.

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<div class="paragraph">

The reasons why Hibernate requires that all entities belonging to an inheritance tree share the same caching definition can be summed as follows:

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<div class="ulist">

• from a performance perspective, adding an additional check on a per entity type level would slow the bootstrap process.

• providing different caching semantics for subclasses would violate the Liskov substitution principle.

  Assuming we have a base class, `Payment` and a subclass `CreditCardPayment`. If the `Payment` is not cacheable and the `CreditCardPayment` is cached, what should happen when executing the following code snippet:

  `Payment payment = entityManager.find(Payment.class, creditCardPaymentId);
  CreditCardPayment creditCardPayment = (CreditCardPayment) CreditCardPayment;`

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  In this particular case, the second level cache key is formed of the entity class name and the identifier:

  `keyToLoad = {org.hibernate.engine.spi.EntityKey@4712}
   identifier = {java.lang.Long@4716} "2"
   persister = {org.hibernate.persister.entity.SingleTableEntityPersister@4629}
    "SingleTableEntityPersister(org.hibernate.userguide.model.Payment)"`

  </div>

  Should Hibernate load the `CreditCardPayment` from the cache as indicated by the actual entity type, or it should not use the cache since the `Payment` is not supposed to be cached?

  </div>

  </td>

  Because of all these intricacies, Hibernate only considers the base class @Cacheable and @Cache definition.

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