[hibernate-dev] Regarding Alex Bacon's "Major issue with Hibernate

[Alex Bacon]

Jeff,

I have been able to get the solution to work using:
- Code generation of Historical Classes using Freemarker
- Hibernate Filters within the Historical Classes to apply the 'as-at'
date
- A Hibernate Event Listener to capture inserts, updates and deletes 
- An AOP interceptor to populate the historical DB
- Hibernate event Listeners to automatically apply the filters when lazy
loading historical entities (not essential but nice to have as it
ensures the filters are on before loading lazy-loaded properties)
- AND (crucially) small changes to two classes - QueryParameters (to fix
the way filters were implemented by removing assumptions about the order
filters appear in the HQL) and EntityJoinWalker (to add in the filters
when lazily loading entities).

Essentially filters are NOT applied when lazily loading entities -
(there is the point of view that this is a bug....as it means you get
different outcomes depending on whether you allow the historical
entities to be all loaded at once or by lazy initialization).    It is
this issue that I fixed with my Hibernate changes.

As you can guess this was a few weeks work - and is not a trivial
afterthought - and I believe better Hibernate support for Historical DBs
would fantastic.   

Alex

-----Original Message-----
From: Drost, Jeff [mailto:Jeff_Drost at adp.com] 
Sent: Wednesday, 17 January 2007 8:23 AM
To: hibernate-dev at lists.jboss.org
Subject: [hibernate-dev] Regarding Alex Bacon's "Major issue with
Hibernate

I have read over these threads and am very interested in doing something
similar.  This is clearly a very common problem.

http://lists.jboss.org/pipermail/hibernate-dev/2006-December/000909.html
http://lists.jboss.org/pipermail/hibernate-dev/2006-September/000267.htm
l

Writing audit state with triggers is a tried and true method, and is
easy to get working.  Reading these records back into a consistent
domain model; now that's magic.  I would like to set a session level
filter parameter with the desired transaction date.  

I have found "something" of a solution, though I'm not sure if it's
taking advantage of a Hibernate feature or a hack.  Hibernate will
correctly substitute filter parameters in conditions that are not part
of filters.  This means you can map where clause on an entity that
refers to a filter parameter. 

@FilterDef(name = "foo", parameters = {@ParamDef(name = "asOfDate", type
= "timestamp")})
@Where(clause = ":foo.asOfDate BETWEEN eff_start_dt and eff_end_dt")

session.enableFilter("foo").setParameter("asOfDate", getAsOfDate());


See also http://forum.hibernate.org/viewtopic.php?t=969798

Thanks,
Jeff
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