I have a normal one:many relationship (IPRouter to configuration) in the database suitable for mapping with the <map> element. However I know that I will only ever retrieve one value from this map: the map-key will be a date, which will always be provided. My current approach is to not provide the getMap() method in the router's interface; I'm storing the relevant date in the router object, and a getConfiguration() method which returns getMap().get(date).

This is working, but it does mean that every configuration is being loaded when I load the router. When I want to compare two configurations, I load the same router twice, once for each date, and compare the two getConfiguration() returns. Effective but highly inefficient.

Is there a way to specify a "dynamic" one-to-one mapping? Something like `where="date=:Date"' in the map? Or maybe a <one-to-one> with a formula that takes a parameter from a query? Some of the routers I'm looking at have hundreds of configurations, and the memory overhead is great enough that I'm considering removing the hibernate map entirely, and implementing this via factory methods.

Would filters be an option you can try? I read from the documentation that you can enable and disable filters too?

Also could you not use a HQL with the "where" condition to get your "Router" objects instead.

You can use a filter. But that might be overkill in this case.

A simpler approach is to use lazy="extra" in Hibernate 3.1.

I'll check out the 3.1 docs to see if that does what I need. I notice that they're not on the documentation page on www.hibernate.org. I can't get the full download until next month (silly international traffic limitations) so I can't say for sure that lazy="extra" is what I want.

I'll read up on filters to pass the time until then :)