Index: lams_common/conf/hibernate/mappings/org/lamsfoundation/lams/learningdesign/Group.hbm.xml
===================================================================
diff -u -r4ec6567d23397141210e7c6979f4293c1d99a5d0 -rd7f8bd90added31c1bbadc8ebd51e301d13965b6
--- lams_common/conf/hibernate/mappings/org/lamsfoundation/lams/learningdesign/Group.hbm.xml	(.../Group.hbm.xml)	(revision 4ec6567d23397141210e7c6979f4293c1d99a5d0)
+++ lams_common/conf/hibernate/mappings/org/lamsfoundation/lams/learningdesign/Group.hbm.xml	(.../Group.hbm.xml)	(revision d7f8bd90added31c1bbadc8ebd51e301d13965b6)
@@ -58,7 +58,6 @@
     <set
         name="users"
         lazy="true"
-        inverse="true"
         cascade="none"
         table="lams_user_group"
     >
Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/ChosenGrouping.java
===================================================================
diff -u -r2eeeb7da6fd05405ea0bdd511270423401536fa9 -rd7f8bd90added31c1bbadc8ebd51e301d13965b6
--- lams_common/src/java/org/lamsfoundation/lams/learningdesign/ChosenGrouping.java	(.../ChosenGrouping.java)	(revision 2eeeb7da6fd05405ea0bdd511270423401536fa9)
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/ChosenGrouping.java	(.../ChosenGrouping.java)	(revision d7f8bd90added31c1bbadc8ebd51e301d13965b6)
@@ -24,5 +24,15 @@
     {
         super(groupingId, groups, activities);
     }
-    
+
+    /**
+     * This type of grouping doesn't have groups other than learner groups.
+     * So it always return <code>true</code>.
+     * @see org.lamsfoundation.lams.learningdesign.Grouping#isLearnerGroup(org.lamsfoundation.lams.learningdesign.Group)
+     */
+    protected boolean isLearnerGroup(Group group)
+    {
+        return true;
+    }
+
 }
Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/Grouping.java
===================================================================
diff -u -r2eeeb7da6fd05405ea0bdd511270423401536fa9 -rd7f8bd90added31c1bbadc8ebd51e301d13965b6
--- lams_common/src/java/org/lamsfoundation/lams/learningdesign/Grouping.java	(.../Grouping.java)	(revision 2eeeb7da6fd05405ea0bdd511270423401536fa9)
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/Grouping.java	(.../Grouping.java)	(revision d7f8bd90added31c1bbadc8ebd51e301d13965b6)
@@ -40,7 +40,7 @@
     private Set activities;
     
     /** non-persistent field */
-    private Set learners;
+    protected Set learners;
     
     /** full constructor */
     public Grouping(Long groupingId, Set groups, Set activities)
@@ -179,16 +179,23 @@
     public Set getLearners()
     {
         //verify pre-condition
-        if(groups==null)
+        if(getGroups()==null)
             throw new IllegalArgumentException("Fail to get learnings from" +
             		"a grouping without groups");
         
         learners = new HashSet();
-        for(Iterator i = groups.iterator();i.hasNext();)
+        for(Iterator i = getGroups().iterator();i.hasNext();)
         {
             Group group = (Group)i.next();
-            learners.addAll(group.getUsers());
+            if(isLearnerGroup(group))
+                learners.addAll(group.getUsers());
         }
         return learners;
     }
+
+    /**
+     * @return
+     */
+    protected abstract boolean isLearnerGroup(Group group);
+
 }
Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/RandomGrouping.java
===================================================================
diff -u -r2eeeb7da6fd05405ea0bdd511270423401536fa9 -rd7f8bd90added31c1bbadc8ebd51e301d13965b6
--- lams_common/src/java/org/lamsfoundation/lams/learningdesign/RandomGrouping.java	(.../RandomGrouping.java)	(revision 2eeeb7da6fd05405ea0bdd511270423401536fa9)
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/RandomGrouping.java	(.../RandomGrouping.java)	(revision d7f8bd90added31c1bbadc8ebd51e301d13965b6)
@@ -61,4 +61,13 @@
         this.numberOfGroups = numberOfGroups;
     }
     
+    /**
+     * This type of grouping doesn't have groups other than learner groups.
+     * So it always return <code>true</code>.
+     * @see org.lamsfoundation.lams.learningdesign.Grouping#isLearnerGroup(org.lamsfoundation.lams.learningdesign.Group)
+     */
+    protected boolean isLearnerGroup(Group group)
+    {
+        return true;
+    }
 }
Index: lams_common/src/java/org/lamsfoundation/lams/lesson/LessonClass.java
===================================================================
diff -u -r2eeeb7da6fd05405ea0bdd511270423401536fa9 -rd7f8bd90added31c1bbadc8ebd51e301d13965b6
--- lams_common/src/java/org/lamsfoundation/lams/lesson/LessonClass.java	(.../LessonClass.java)	(revision 2eeeb7da6fd05405ea0bdd511270423401536fa9)
+++ lams_common/src/java/org/lamsfoundation/lams/lesson/LessonClass.java	(.../LessonClass.java)	(revision d7f8bd90added31c1bbadc8ebd51e301d13965b6)
@@ -48,4 +48,17 @@
 	public void setLesson(Lesson lesson) {
 		this.lesson = lesson;
 	}
+
+    /**
+     * @see org.lamsfoundation.lams.learningdesign.Grouping#isLearnerGroup(org.lamsfoundation.lams.learningdesign.Group)
+     */
+    protected boolean isLearnerGroup(Group group)
+    {
+        if(group.getGroupId()==null||staffGroup.getGroupId()==null)
+            throw new IllegalArgumentException("Can't check up whether group" +
+            		" is learner group without group id.");
+        
+        return staffGroup.getGroupId()!=group.getGroupId();
+    }
+
 }
\ No newline at end of file
Index: lams_common/test/java/org/lamsfoundation/lams/lesson/TestLessonClass.java
===================================================================
diff -u
--- lams_common/test/java/org/lamsfoundation/lams/lesson/TestLessonClass.java	(revision 0)
+++ lams_common/test/java/org/lamsfoundation/lams/lesson/TestLessonClass.java	(revision d7f8bd90added31c1bbadc8ebd51e301d13965b6)
@@ -0,0 +1,81 @@
+/* ********************************************************************************
+ *  Copyright Notice
+ *  =================
+ * This file contains propriety information of LAMS Foundation. 
+ * Copying or reproduction with prior written permission is prohibited.
+ * Copyright (c) 2005 
+ * Created on 14/02/2005
+ ******************************************************************************** */
+
+package org.lamsfoundation.lams.lesson;
+
+import java.util.HashSet;
+
+import org.lamsfoundation.lams.learningdesign.Group;
+import org.lamsfoundation.lams.usermanagement.User;
+
+import junit.framework.TestCase;
+
+
+/**
+ * 
+ * @author Jacky Fang 14/02/2005
+ * 
+ */
+public class TestLessonClass extends TestCase
+{
+
+    LessonClass lessonClass;
+    /*
+     * @see TestCase#setUp()
+     */
+    protected void setUp() throws Exception
+    {
+        super.setUp();
+        lessonClass = new LessonClass();
+        lessonClass.setGroups(new HashSet());
+    }
+
+    /*
+     * @see TestCase#tearDown()
+     */
+    protected void tearDown() throws Exception
+    {
+        super.tearDown();
+    }
+
+    /**
+     * Constructor for TestLessonClass.
+     * @param arg0
+     */
+    public TestLessonClass(String arg0)
+    {
+        super(arg0);
+    }
+
+    public void testGetLearners()
+    {
+        User user1 = new User();
+        user1.setUserId(new Integer(1));
+        Group group1 = new Group();
+        group1.setGroupId(new Long(1));
+        group1.setUsers(new HashSet());
+        group1.getUsers().add(user1);
+        group1.setOrderId(lessonClass.getNextGroupOrderId());
+        lessonClass.getGroups().add(group1);
+        
+        User staff = new User();
+        staff.setUserId(new Integer(3));
+        Group staffGroup = new Group();
+        staffGroup.setGroupId(new Long(2));
+        staffGroup.setUsers(new HashSet());
+        staffGroup.getUsers().add(staff);
+        staffGroup.setOrderId(lessonClass.getNextGroupOrderId());
+        lessonClass.getGroups().add(staffGroup);
+        lessonClass.setStaffGroup(staffGroup);
+        
+        assertEquals("verify number of learners",1,lessonClass.getLearners().size());
+
+   }
+
+}