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The Hibernate entity mappings for the logged PortalEvents is done in the file uportal-impl/src/main/resources/properties/db/stats/portalEvents.hbm.xml. If you add a new PortalEvent implementation that should be logged to the database it needs to be mapped correctly in this file. Unmapped PortalEvents are ignored by the database logging code.
Reading Events
The Hibernate entity mappings and PortalEvent classes are not designed to be read from the database using Hibernate, only to be a logging facility. Any reporting tools should just use straight SQL as doing large reporting tasks via ORM is not easy and the PortalEvent object model is not designed for such use.