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

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The following comment has been added to this issue:

     Author: Marko Nikolic
    Created: Mon, 1 Sep 2003 7:43 AM
       Body:
Well, then 'Lightweight Class' should be removed from documentation ;) What is the way to do something similar? Maybe including blob column in select does not impact performance so much if you don't use Blob.getBinaryStream() on it? Is stream to blob opened when you issue select, or only when you ask for stream, or is that depending on jdbc driver implementation?
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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:
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        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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