Re: [xwiki-devs] [Proposal] Implementation for XWIKI-8271 (extensible Hibernate mappings)

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