Index inheritance is a nice feature for the case when you have several sub-classes inheriting from a common base class and you want to lookup instances by a slot value regadless of the sub-class. E.g. if super-from and mega-frob inherit from frob base class you can look up any kind of frob by frob-id if it is inherited.
But what's about the case where you want to be able to do queries both among all subclasses and for a specific sub-class? id slot is probably a bad example since it is likely to be unique, so let's say we have frob-style slot. Sometimes I want get any kind of frob with a specific style: (ele:get-instances-by-value 'frob 'frob-style "vanilla") Sometimes I want to get instances of a specific class with a certain property: (ele:get-instances-by-value 'super-frob 'frob-style "vanilla") But if slot frob-style has inherited index it doesn't matter what specific class is passed to get-instances-by-value, it can return frobs and mega-frobs even if you're asking for super-frobs. I think ideally this would be resolved with a new type of 'hierarchical' slot indices where instances will be indexed in many indices at once -- when you make super-frob instance it will be indexed by frob-style both in super-frob and frob index (and, generally, in all super-classes). In this case get-instances-by-... semantics will be cleaner. But perhaps that would be rather hard to implement. As a quick fix, maybe we can filter instances on get-instances-by-... or map-inverted-index level? These functions have information about actual class so filtering instances using type-of should be trivial. Of course that will have sub-optimal performance as more instances will be pulled from database. But it is better than nothing and it fixes non-intuitive behaviour (instances of wrong type are returned if you look at it from API point of view). Users might achieve this functionality using derived indices -- say, normal frob-style slot won't have inherited index but derived slot frob-style* will be inherited and will just mirror frob-style. Thus when you want to lookup among all sub-classes you should use frob-style* instead of frob-style. But this looks a bit cumbersome in class definitions. _______________________________________________ elephant-devel site list elephant-devel@common-lisp.net http://common-lisp.net/mailman/listinfo/elephant-devel
