a first implementation draft for grails/gorm-hibernate5#63

[zyro23]

review/feedback would be appreciated. some things to note:

• this branch originates from the 6.1.x branch and this pr also targets 6.1.x. that is because i was not able to build/publish the grails-data-mapping master locally. not sure if there is wip going on?
  • if i should rebase onto master (this can be considered an enhancement/feature) and pr to master please say so and i will further investigate whats going on with master
• i did not involve HibernateConnectionSource or AbstractHibernateDatastore in the implementation intentionally
  • those reside in grails-data-mapping-hibernate-core and I am not sure whats the current state there reg. compatibility with hibernate 3/4 vs. hibernate-5.2-only.
• maybe there is a better way to expose the Metadata (instead of using HibernateDatastore)?
• maybe there is a better way to pass the Metadata from the MetadataIntegrator to the place where it is exposed, instead of relying on a hibernate service registry lookup?
• if the current implementation is considered "ok", should HibernateDatastore.getMetadataInternal() remain private or better be declared protected?

i welcome any corrections/suggestions/improvements.

thank you!

[graemerocher]

Looks ok to me.. don't see a reason why it should be changed from private

[zyro23]

cool, thanks. i will update the pull-request so that the hibernate5 grails plugin uses the exposed metadata for schemaExport and then i hope this is ready to merge.