Allow mixing <union-subclass>and <subclass> ------------------------------------------- Key: HHH-1233 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-1233 Project: Hibernate3 Type: Improvement

Components: core Environment: N/A Reporter: Gunther Schadow

BACKGROUND: Hibernate allows mixing <subclass> and <joined-subclass> inheritance mappings but apparently not <subclass> and <union-subclass> mappings, however, this seems like the most useful combination. Example: USE CASE: We may have a hierarchy with very unevenly distributed mass, i.e., some subclasses have millions of objects, others have only a half-dozen. There may be a lot of different subclasses of the smaller sort. Union-subclass seems ideal to work with a dozen different humongous tables, as they can be placed on different tablespaces and managed differently. However, for the 200 or so subclasses whith only a dozen objects each, it would be easier to map these into a single table per sub-hierarchy. REQUESTED FEATURE: Therefore it seems fair to suggest that <subclass> mappings should be supported underneath <union-subclass> mappings. To allow that the <discriminator> element would have to be handled inside a <union-subclass> element and same for the discriminator-value attribute. Perhaps one could limit the complexity by requiring that the outer mapping must be union-subclass and the inner can be subclass but not vica versa? WORKAROUNDS: As the documentation mentions one could just create several independent <class> hierarchies, thus effectively emulating the first level of union-subclass specializations. But that would not allow specifying polymorphic associations. ESTIMATED EFFORT: It could be difficult to implement support for this. But would like to know whether this is something that is somewhere on the radar screen for the future.