Andy Jefferson created JDO-764:
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Summary: Allow JDO annotations to be used in meta-annotations
Key: JDO-764
URL: https://issues.apache.org/jira/browse/JDO-764
Project: JDO
Issue Type: Improvement
Components: api
Reporter: Andy Jefferson
By default annotations are used directly in a persistable class. Java
additionally allows annotations to be formed of other annotations. This is
particularly useful where a user has a particular combination of annotations to
set on a class/field/method and wants to simply annotate with an abbreviated
form. For example, specifying attributes of an annotation
@PersistenceCapable(detachable="true", identityType="datastore",
embeddedOnly="true")
or formed of multiple annotations
@PersistenceCapable(detachable="true")
@Extension(vendorName="datanucleus", key="multitenancy-column-name",
value="TENANT")
These can be represented as meta-annotations like this
@Target(TYPE)
@Retention(RUNTIME)
@PersistenceCapable(detachable="true", identityType="datastore",
embeddedOnly="true")
@interface @DatastoreIdPersistable
{
}
@Target(TYPE)
@Retention(RUNTIME)
@PersistenceCapable(detachable="true")
@Extension(vendorName="datanucleus", key="multitenancy-column-name",
value="TENANT")
@interface @MultitenantPersistable
{
}
and the user can subsequently just annotate their persistable class as
@DatastoreIdPersistable
public class MyClass1 {...}
@MultitenantPersistable
public class MyClass2 {...}
The work required to support this in the JDO spec is simply to update the
following annotations to add @Target({ElementType.ANNOTATION_TYPE})
The annotations requiring this are
@Element, @EmbeddedId, @Key, @NotPersistent, @Order, @Persistent, @Serialized,
@Transactional, and @Value (all other annotations already have
@Target({ElementType.TYPE}) which already permits their usage in
meta-annotations.
The same is proposed for JPA 2.2, see
https://github.com/javaee/jpa-spec/issues/43
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