Bug 201038 The joint dataset from library can not be used and exception occurs when preview in dataset[07]
Description: The joint dataset from library can not be used and exception occurs when preview in dataset[07] Build number: 2.2.1.v20070824-0630 Steps to reproduce: 1, New a library and create two datasets ds1 and ds2 2, Creata a joint dataset ds3 using ds1 and ds2 3, Publish the library 4, New a report and using the Joint dataset and preview in joint dataset Expected result: The preview should be successful Actual result: Exception occurs Error log: java.lang.ClassCastException: org.eclipse.birt.report.model.metadata.ElementRefValue at org.eclipse.birt.report.model.command.AbstractPropertyCommand.setupStructureContext(AbstractPropertyCommand.java:534) at org.eclipse.birt.report.model.command.AbstractPropertyCommand.makeLocalCompositeValue(AbstractPropertyCommand.java:440) at org.eclipse.birt.report.model.command.ComplexPropertyCommand.doRemoveItem(ComplexPropertyCommand.java:456) at org.eclipse.birt.report.model.command.ComplexPropertyCommand.removeItem(ComplexPropertyCommand.java:393) at org.eclipse.birt.report.model.api.PropertyHandle.removeItem(PropertyHandle.java:317) at org.eclipse.birt.report.model.api.SimpleValueHandle.removeItem(SimpleValueHandle.java:453) at org.eclipse.birt.report.model.api.JointDataSetHandle.removeDataSet(JointDataSetHandle.java:128) at org.eclipse.birt.report.designer.data.ui.dataset.JointDataSetPage.modifyJointCondition(JointDataSetPage.java:989) at org.eclipse.birt.report.designer.data.ui.dataset.JointDataSetPage.canLeave(JointDataSetPage.java:963) at org.eclipse.birt.report.designer.data.ui.property.AbstractPropertyDialog.showPage(AbstractPropertyDialog.java:554) at org.eclipse.birt.report.designer.data.ui.property.AbstractPropertyDialog.showSelectionPage(AbstractPropertyDialog.java:467) at org.eclipse.birt.report.designer.data.ui.dataset.DataSetEditor.showSelectionPage(DataSetEditor.java:820) at org.eclipse.birt.report.designer.data.ui.property.AbstractPropertyDialog$3.run(AbstractPropertyDialog.java:425)
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/AbstractPropertyCommand.java
* Justifies whether the extended element is created if the UI invokes some
	 * operations to change the extension properties.
	 * 
	 * Note that <code>PropertyCommand</code> do not support structure
	 * operations like addItem, removeItem, etc. for extension elements. This
	 * method is kept but NERVER call it in <code>doSetProperty</code>.
	 * 
	 * @param module
	 *            the module
	 * @param element
	 *            the extended item that holds the extended element
	 * @param prop
	 *            the extension property definition to change
	 */
	protected void assertExtendedElement( Module module, DesignElement element,
			PropertyDefn prop )
	{
		if ( element instanceof ExtendedItem )
		{
			ExtendedItem extendedItem = (ExtendedItem) element;
			if ( extendedItem.isExtensionModelProperty( prop.getName( ) )
					|| extendedItem.isExtensionXMLProperty( prop.getName( ) ) )
			{
				assert ( (ExtendedItem) element ).getExtendedElement( ) != null;
			}
		}
	}
	/**
	 * Validates the values of the item members.
	 *