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https://issues.apache.org/jira/browse/JDO-615?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12653493#action_12653493
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Craig Russell commented on JDO-615:
-----------------------------------
> Re: priority of user-defined metadata.
> Why not make user-defined metadata highest priority? That way the user has a
> way of overriding some package.jdo in the CLASSPATH which they can treat as
> their fallback.
The rationale for the algorithm used today is that once metadata has been
defined, there may be other metadata that depends on it (e.g. inheritance and
relationships). So if you change this you are in danger of breaking things that
are working for other parts of the application. I don't have a use-case for
changing metadata that's already been defined. Do you?
> Other item : do we want to provide access to metadata for a class being used
> by the persistence process ? I'd favour something simple like ClassMetadata
> pmf.getMetadata(String classname);
> This will allow applications to access mapping info (e.g table used for a
> class) and utilise it in a different part of their app. Obviously it would be
> down to individual implementations whether they support any subsequent
> changes to that metadata if handed out to the user.
There are two questions: do we support a way for an application to get the
current definition of metadata? I'd say yes.
Do we support changing metadata by modifying the metadata objects that are
given to the application? Without a clear understanding of the use-case for
this (see above) I'd say no thanks. The metadata instances should be immutable
if given out, or at least give out a copy of what's defined, that by definition
doesn't change the current copy. Seems like it's "easy enough" to copy
metadata.
Yet another more topic: security. We probably need to add a security bit to the
registerMetadata and getMetadata calls. We already have the getMetadata
permission but might want a setMetadata permission as well.
> MetaData specification API
> --------------------------
>
> Key: JDO-615
> URL: https://issues.apache.org/jira/browse/JDO-615
> Project: JDO
> Issue Type: New Feature
> Reporter: Andy Jefferson
> Fix For: JDO 2 maintenance release 3
>
> Attachments: jdometadata-5.patch
>
>
> We can specify MetaData via XML or annotations. The only way missing is via
> an API. I propose mirroring the XML structure with interfaces of the form
> public interface MetaData
> {
> addExtension(String key, String value);
> removeExtension(String key, String value);
> ...
> }
> public interface FileMetaData
> {
> addPackage(PackageMetaData pmd);
> ...
> }
> public interface PackageMetaData
> {
> addClass(ClassMetaData cmd)
> ...
> }
> public interface ClassMetaData
> {
> addField(FieldMetaData fmd)
> ...
> }
> public interface FieldMetaData
> {
> setInheritance(InheritanceMetaData inhmd)
> ...
> }
> and so on.
> We would then require a method on the PMF to register the metadata.
> If there are no objections to such a feature I'll propose a patch to try to
> provide all current JDO2 capabilities.
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