Hi, with great interest I read that Hibernate now has an approach for QBE. That is wonderful. However I could not find it mentioned while searching the documentation or the Hibernate site (apart from the announcement in the news-section.) I only found a short example in the API doc for the Example class but that still leaves some questions open.

Particularly I wonder how relationships are handled in the QBE case. Also, how can user-defined types be used for subsumption style mapping? I don't expect all of this to exist, but would appreciate some explanation to the approach and the roadmap.

Thanks,
-Gunther

See http://www.hibernate.org/hib_docs/reference/html/query-criteria.html#query-criteria-s6 - Version properties, identifiers and associations are ignored. You can however place criterias upoon associated objects using the Example API, see the URL.

What do you men by "subsumption style mapping?"

O.K. thanks. Well, it seems as if it ought to be relatively easy to extend
the Example criteria by automatically walking and including associated
objects. That's wonderful.



Did I say "mapping", oops. I meant subsumption style querying. By that I mean that a QBE approach is most powerful if you interpret the supplied values as value classes and your query is trying to find anything subsumed by those value classes. That's what you intuitively do with the "case-insensitive" and "like" comparison on string fields. For numeric fields you really want to have something like that too. E.g., you want to put "<5" in a field to match all values less than 5.

The most systematic way of doing this that I know of is to consider all numeric values as intervals. Then you can just supply an interval in the QBE Example field and that matches all subsets. To do this, I need to use a user-extension data type, interval. This needs to be supported on the SQL side as well. When I looked at user-type support in hibernate a year ago or so ago, there were some difficulties with mapping operations such as "subset-of" in SQL... but I can't remember the specifics now.

You also have subsumption semantics for queries on nominal-coded fields, particularly if you have a code system with specializations.

It's great that hibernate is on the right track with the QBE, it can probably become extremely powerful.

regards,
-Gunther

Has any consideration been giving for adding the ability for QBE to include associations? If not, can someone share their code that walks the associations and includes them in the generated SQL?

Thanks,
James

hibernate in action

you have details for managing association via criteria
mix criteria.createCriteria + QBE