@Persist("entity") will store the id in the HttpSession and then lookup the
entity from the db any time it's required. In 99% of cases, you can avoid
HttpSession usage all together. By using @PageActivationContext or
onActivate() / onPassivate() you can pass the id in the URL and avoid
HttpSession usage all together. This has the added benefit that your users
can open multiple windows viewing two different entities and it still
works.
The one thing that I do store in the HttpSession is the logon id of the
user but that's about it.
