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Key: HB-286
Summary: Support for discriminator when using <joined-subclass>
Type: New Feature
Status: Unassigned
Priority: Major
Project: Hibernate2
Components:
core
Versions:
2.0.2
Assignee:
Reporter: Kenneth Foo
Created: Sat, 23 Aug 2003 9:35 PM
Updated: Sat, 23 Aug 2003 9:35 PM
Environment: Windows XP Pro, JDK 1.4.2, Hibernate 2.0.2, HSQLDB 1.7.1
Description:
Descriminators are only available when using <subclass>, but
not currently supported when using <joined-subclass>.
For performance reasons, would be great if <joined-subclass> supported this too.
Assume the following class hierarchy
class A;
class B extends A;
class C extends A;
class D extends A;
class E extends A;
An ID named "id" is defined in A.
In my object model, there are MANY classes which derive from A.
We map them as table-per-class using <joined-subclass>.
When <joined-subclass> is used (due to database limitation, I HAVE to use this), Hibernate issues a query which involves multiple joins across the table. This is inefficient as it might involve multiple table locks/index scans on some databases. It is made even worse when we have an object model where there are many derivatives of A.
I propose that discriminators are allowed in such a condition such that the unnecessary joins and lookups are avoided.
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