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https://issues.apache.org/jira/browse/JDO-764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16032931#comment-16032931
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Andy Jefferson commented on JDO-764:
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API updated with the patch. Spec updated to mirror the updates to the various
annotations.
Whether it needs any more than that in the spec is left for others to decide.
For reference I added a block to the DataNucleus documentation at
http://www.datanucleus.org/products/accessplatform_5_0/jdo/annotations.html#meta_annotations
explaining about meta-annotations and that JDO annotations can be utilised.
> 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, specification
> Affects Versions: JDO 3.1
> Reporter: Andy Jefferson
> Fix For: JDO 3.2
>
> Attachments: JDO-764.patch
>
>
> 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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