[Hibernate-issues] [Hibernate-JIRA] Closed: (HB-301) Lightweight design pattern does not work (WrongClassException)

[<leg...@at...>]

Message:

   The following issue has been closed.

   Resolver: Gavin King
       Date: Mon, 1 Sep 2003 6:23 AM

This is not a bug. This is correct behaviour.
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View the issue:

  http://opensource.atlassian.com/projects/hibernate/secure/ViewIssue.jspa?key=HB-301


Here is an overview of the issue:
---------------------------------------------------------------------
        Key: HB-301
    Summary: Lightweight design pattern does not work (WrongClassException)
       Type: Patch

     Status: Closed
   Priority: Major
 Resolution: REJECTED

    Project: Hibernate2
 Components: 
             core
   Versions:
             2.0.2
             2.0.3

   Assignee: 
   Reporter: Marko Nikolic

    Created: Sun, 31 Aug 2003 10:31 AM
    Updated: Mon, 1 Sep 2003 6:23 AM
Environment: Windows XP, JDK 1.4.2, Jetty 4.2.3

Description:
I am having problem using Lightweight design pattern. I must admit that I am completely new to Hibernate but it seems to me like this is a bug of Hibernate.

Here are my mappings:

### FileInfo.hbm.xml ###
<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 2.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
    <class name="com.redstarshop.data.FileInfo" table="files">
        <id name="id" column="id" type="long">
            <generator class="native"/>
        </id>
        <property name="name" column="name"/>
        <property name="contentType" column="content_type" not-null="true"/>
        <property name="length" not-null="true" column="content_length"/>
        <property name="lastModified" column="last_modified" not-null="true"/>
	</class>
</hibernate-mapping>

### File.hbm.xml ###
<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 2.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
    <class name="com.redstarshop.data.File" table="files" polymorphism="explicit">
        <id name="id" column="id" type="long">
            <generator class="native"/>
        </id>
        <property name="name" column="name"/>
        <property name="contentType" column="content_type" not-null="true"/>
        <property name="length" not-null="true" column="content_length"/>
        <property name="lastModified" column="last_modified" not-null="true"/>
        <property name="content" not-null="true"/>
	</class>
</hibernate-mapping>

### End of mappings ###

Now, loading FileInfo (lightweight) entity works fine. But if I try to load File (heavyweight) entity (after FileInfo was loaded and cached) with the same id as loaded FileInfo, using either:

session.load(File.class, id)

or

session.find("from com.redstarshop.data.File as c where c.id = ?", id, Hibernate.LONG)

I always get

net.sf.hibernate.WrongClassException: Object with id: 12 was not of the specified subclass: com.redstarshop.data.File (loaded object was of wrong class)
	at net.sf.hibernate.loader.Loader.instanceAlreadyLoaded(Loader.java:300)
	at net.sf.hibernate.loader.Loader.getRow(Loader.java:278)
	at net.sf.hibernate.loader.Loader.doFind(Loader.java:159)
	at net.sf.hibernate.loader.Loader.find(Loader.java:620)
	at net.sf.hibernate.hql.QueryTranslator.find(QueryTranslator.java:928)
	at net.sf.hibernate.impl.SessionImpl.find(SessionImpl.java:1343)
	at net.sf.hibernate.impl.SessionImpl.find(SessionImpl.java:1322)
	at net.sf.hibernate.impl.SessionImpl.find(SessionImpl.java:1318)
	at com.redstarshop.util.Utils.findOne(Utils.java:46)
	at com.redstarshop.tapestry.FileService.service(FileService.java:116)
	at org.apache.tapestry.engine.AbstractEngine.service(AbstractEngine.java:913)
	at org.apache.tapestry.ApplicationServlet.doService(ApplicationServlet.java:238)
	at org.apache.tapestry.ApplicationServlet.doGet(ApplicationServlet.java:199)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
	at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:366)
	at org.mortbay.jetty.servlet.WebApplicationHandler$Chain.doFilter(WebApplicationHandler.java:341)
	at org.apache.tapestry.RedirectFilter.doFilter(RedirectFilter.java:148)
	at org.mortbay.jetty.servlet.WebApplicationHandler$Chain.doFilter(WebApplicationHandler.java:333)
	at org.mortbay.jetty.servlet.WebApplicationHandler.dispatch(WebApplicationHandler.java:285)
	at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:567)
	at org.mortbay.http.HttpContext.handle(HttpContext.java:1696)
	at org.mortbay.jetty.servlet.WebApplicationContext.handle(WebApplicationContext.java:552)
	at org.mortbay.http.HttpContext.handle(HttpContext.java:1646)
	at org.mortbay.http.HttpServer.service(HttpServer.java:884)
	at org.mortbay.http.HttpConnection.service(HttpConnection.java:799)
	at org.mortbay.http.HttpConnection.handleNext(HttpConnection.java:949)
	at org.mortbay.http.HttpConnection.handle(HttpConnection.java:816)
	at org.mortbay.http.SocketListener.handleConnection(SocketListener.java:204)
	at org.mortbay.util.ThreadedServer.handle(ThreadedServer.java:290)
	at org.mortbay.util.ThreadPool$PoolThread.run(ThreadPool.java:509)


Following patch against 2.0.3 works fine for me (I patched loader to use fetched instance only if it is assignable to requested type).

### Begin of patch ###
--- /cygdrive/c/java/hibernate-2.0.3/src/net/sf/hibernate/loader/Loader.java	2003-08-27 16:49:40.000000000 +0200
+++ hibernate-2.0.3/src/net/sf/hibernate/loader/Loader.java	2003-08-31 17:03:34.000000000 +0200
@@ -273,7 +273,7 @@ public abstract class Loader {
 				
 				//If the object is already loaded, return the loaded one
 				object = session.getEntity(key);
-				if (object!=null) {
+				if (object!=null && persisters[i].getMappedClass().isAssignableFrom(object.getClass())) {
 					//its already loaded so don't need to hydrate it
 					instanceAlreadyLoaded(rs, i, persisters[i], suffixes[i], key, object, lockModes[i], session);
 				}
@@ -296,9 +296,6 @@ public abstract class Loader {
 	private void instanceAlreadyLoaded(ResultSet rs, int i, Loadable persister, String suffix, Key key, Object object, LockMode lockMode, SessionImplementor session) 
 	throws HibernateException, SQLException {
 		
-		if ( !persister.getMappedClass().isAssignableFrom( object.getClass() ) )
-			throw new WrongClassException( "loaded object was of wrong class", key.getIdentifier(), persister.getMappedClass() );
-	
 		if ( LockMode.NONE!=lockMode && upgradeLocks() ) { //no point doing this if NONE was requested
 
 			if ( 
### End of patch ###



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