From: Alex Young <alex@...>
Date: 2006-06-28T22:03:18+09:00
Subject: Re: How to model Hibernate multi-table inheritance with ActiveRecord?

Marcus Andersson wrote:
> Hi
> 
> I have this "old" database mainly modeled for Hibernate. The java model 
> has something called Asset. Asset is inherited by SomeAsset and 
> AnotherAsset and the similar stuff is in the asset table and the 
> specific data for SomeAsset is in table some_asset and for AnotherAsset 
> in another_asset. This is then reflected in hibernate using a 
> <joined-subclass/> element.
> 
> What would be the best way to model this in ActiveRecord? I cannot 
> change the exisiting database structure beyond adding new columns (ie I 
> cannot move values from the join tables back to the main table and use 
> STI).
> 
> Could I implement method_missing in Asset to just delegate to methods 
> that might exist in SomeAsset or AnotherAsset? I only use duck typing so 
> from a type perspective it would be fine. This would make it hard to 
> override behaviour from Asset in subclasses though (since they aren't 
> subclasses...).
> 
> Is there another better solution?
I'd have SomeAsset and AnotherAsset instances each hold a delegate Asset 
object that they proxy any calls they can't answer themselves to.  I've 
played around a little with trying to implement a full class table 
inheritance scheme for AR on that basis, but never really had enough 
need for it myself to polish it up.

-- 
Alex