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https://issues.apache.org/jira/browse/JDO-764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16036379#comment-16036379
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Craig L Russell commented on JDO-764:
-------------------------------------
Do we have any test classes that could easily be adapted to test this
capability? We could perhaps define these annotations as one and use in several
places in the test cases:
@Target(TYPE)
@Retention(RUNTIME)
@PersistenceCapable(detachable="true", identityType="datastore",
embeddedOnly="true")
@Inheritance(strategy=InheritanceStrategy.NEW_TABLE)
@Discriminator(strategy=DiscriminatorStrategy.CLASS_NAME,
column="DISCRIMINATOR", indexed="true")
@DatastoreIdentity(strategy=IdGeneratorStrategy.IDENTITY,
column="DATASTORE_IDENTITY")
@interface @DatastoreIdDiscriminatorPersistable { }
Then:
@PersistenceCapable(table="persons")
@DatastoreIdDiscriminatorPersistable
public class FCDSPerson
implements IPerson, Serializable, Comparable, Comparator, DeepEquality {
Here is additional text to be added to Chapter 19 of the specification. Please
review, especially the terminology "compound annotations".
Annotations can be combined and applied to user-defined compound annotations. A
user-defined annotation itself can be annotated with one or more JDO
annotations and when the user-defined annotation is applied to an element, all
of its JDO annotations will be applied to that element.
> 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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