[Hibernate-issues] [Hibernate-JIRA] Closed: (HB-282) JCS: Routing *different* classes to *same* JCS Region causes ClassCastException

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Message:

   The following issue has been closed.

   Resolver: Gavin King
       Date: Fri, 22 Aug 2003 1:25 PM

This is not a bug; this is how it is designed.
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View the issue:

  http://opensource.atlassian.com/projects/hibernate/secure/ViewIssue.jspa?key=HB-282


Here is an overview of the issue:
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        Key: HB-282
    Summary: JCS: Routing *different* classes to *same* JCS Region causes ClassCastException
       Type: Bug

     Status: Closed
   Priority: Major
 Resolution: REJECTED

    Project: Hibernate2
 Components: 
             core
   Versions:
             2.1
             2.0.1
             2.0.2
             2.1 beta 1

   Assignee: 
   Reporter: Bertrand Renuart

    Created: Fri, 22 Aug 2003 5:09 AM
    Updated: Fri, 22 Aug 2003 1:25 PM

Description:
Summary:
--------
Configuring two classes to share the same JCS Region may cause ClassCastException on cache hit.


Description:
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By default, Hibernate will use different cache regions for each class, the region name being the class name (class name + property path for collections).
When using the cache config inside hibernate.cfg.xml, it is possible to specify in which region each class should endup. This way, it is possible to direct different classes to the same region.

Internally, Hibernate creates a JCSCache proxy for each class, with a reference to the underlying JCS Region.
If two classes share the same region, then two Hibernate JCSCache proxies are created, both pointing to the same JCS Region.

Object are put and retrieved in/from JCS using a *key*. 
Hibernate uses the persistent ID of the class as key (the Serializable than can be used the load() the object).

Unfortunately, instances of different classes may have the same ID (say a Long if you use the Increment generator). 
If they share the same cache region, one instance will override the other (the cache behaves like a Java Map) - confusing Hibernate on retrieve from cache and causing a ClassCastException (either in your code when casting the return of load(), or inside Hibernate in case of collections).




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