Classcastexception when requesting database object from an upgraded extension

Hibernate is initialized at startup and extension having database mapping are also injecting their mapping at startup. The problem is that if you upgrade the extension then the classes Hibernate knows are the one from the previous classloader.

Ideally, we would need to recreate the Hibernate classloader as soon as the classloader of any of the currently registered hibernate entities is closed. There does not seems to be any way to know that in standard ClassLoader but we could add a #isClosed() in NamespaceURLClassLoader.

The workaround is to restart XWiki.