[Hibernate-issues] [Hibernate-JIRA] Created: (HB-286) Support for discriminator when using <joined-subclass>

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  A new issue has been created in JIRA.

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  http://opensource.atlassian.com/projects/hibernate/secure/ViewIssue.jspa?key=HB-286


Here is an overview of the issue:
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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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