Hi Andreas, On Oct 3, 2012, at 9:22 AM, Andreas Jonsson <[email protected]> wrote:
+1 for extensible entity mappings.
When registering a new mapping, i think that it should be possible to specify if it should apply to a particular wiki or to the whole farm. The collection of mappings for the whole farm should of course be enabled for new wiki instances.
Indeed that's a possibility and it'll almost work OOB with my proposal since an extension can be installed only on a subwiki for ex. However it would also require: * ability to register core extensions for a given wiki * have a session factory per wiki And that's more complex. I'd like to finish my refactoring first and this could be added later on if we agree about it since it won't impact much what I'm working on. (see below)
While we are at it, we should try to find a better way to implement virtual wikis. As I've already mentioned, I believe that this can be achieved by reregistering entity mappings per wiki, with prefixed entity names. (This would really be the same as extensible entity mappings.) It seems that this should enable access to multiple wikis within the same Hibernate session, while being fully backwards compatible with the current implementation.
But Denise wrote "[...] I doubt you will reach soon a state where hibernate support sessions across databases." and I'm not sure if he knows something about Hibernate limitations that would prevent this solution.
The XML-schema for entity mappings allows for both a schema and catalog attributes to the class element. If this is implemented in the expected way, it should work to use mapping templates such as:
<class name="${entityNamePrefix}:com.xpn.xwiki.doc.XWikiDocument" table="xwikidoc" schema="${entitySchemaAttribute}">
and for MySQL
<class name="${entityNamePrefix}:com.xpn.xwiki.doc.XWikiDocument" table="xwikidoc" catalog="${entityCatalogAttribute}">
And then you implement an EntityNamingStrategy for selecting the correct mappings for the current wiki.
BTW another solution could be to not any issue any schema change but to have hibernate prefix all queries with the schema/catalog/user, e.g. "select * from <dbname>.<table>". I couldn't find any built in support for this but it could be possible to plug a new strategy - would need to ask them. Thanks -Vincent
Best Regards,
/Andreas
2012-10-02 20:53, Vincent Massol skrev:
Hi devs,
I'd like to propose the following to implement http://jira.xwiki.org/browse/XWIKI-8271:
* Create a new xwiki-platform-store-hibernate module * Add a Component role: HibernateConfiguration implements Comparable * API: void HibernateConfiguration.configure(Configuration aggregatedConfiguration), where the passed aggregatedConfiguration contains the configuration filled by all the HibernateConfiguration.configure() calls executed before * Add a HibernateConfigurationManager.getConfiguration() component that is in charge of loading the various HibernateConfiguration in the correct order * Have an AbstractHibernateConfiguration implements HibernateConfiguration with 1 API: getDatabaseType(Configuration configuration). It gets the DB type from the connection URL string and returns a DatabaseType object which represents the database type
* CoreHibernateMapping (hint = "xwiki") <==> xwiki.hbm.*.xml - highest priority, defines the connection URL among other props * ActivityStreamHibernateMapping (hint = "activitystream") * FeedHibernateMapping (hint = "feeds")
Note 1: If a HibernateConfiguration impl needs to load mappings that depend on the DB they call AbstractHibernateConfiguration. getDatabaseType() to get the DB. Note 2: If the user wants to use a different HBM file, he/she just has to put a file with the same name (e.g. xwiki.hbm.xml) in WEB-INF/classes Note 3: This means we won't put any mapping anymore in the hibernate.cfg.xml file since it's not needed anymore (although it would continue to work if you put mappings there).
Usage:
@Inject HibernateConfigurationManager configurationManager;
Configuration configuration = configurationManager.getConfiguration(); SessionFactory sessionFactory = configuration.buildSessionFactory();
Then all that remains to implement http://jira.xwiki.org/browse/XWIKI-8271 is to have a component singleton that will be in charge of returning the SessionFactory and which can be asked to rebuild a new SessionFactory (using a new Configuration).
We'll just need to decide how we trigger this. 2 options: * By using an Event Listener listening on HibernateConfiguration registrations and recreating automatically a new SessionFactory when it happens. Cons: if an extension contributes several HibernateConfiguration then Hibernate will be reinitialized several times * By listening to an Event sent by the Extension Manager when an extension has finished loading and somehow find out all the HibernateConfiguration that have been added (several ways of doing this) and recreating the SessionFactory
Note: The only issue I can foresee is if a Hibernate call is in progress in one thread when an extension is installed and a new SessionFactory is created at the same time. Either we don't care or we could implement retry at the DB level, or we could introduce some semaphore so that we start the reinit only when nobody has a lock on the SessionFactory, or…
WDYT?
Of course, the pros is those listed in http://jira.xwiki.org/browse/XWIKI-8271: * Ability for a platform module to contribute Hibernate mappings (static) * Ability for an extension installed at runtime to contribute Hibernate mappings (dynamic)
Note that the reason I'm starting all this is because I'd like to implement http://jira.xwiki.org/jira/browse/XWIKI-7953 cleanly in a module separate from oldcore.
Thanks -Vincent