－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－
database table：
Users:
userId not null int primary key
...
SystemMenu:
menuId not null int primary key
...
user_menu:(the map of Users and SystemMenu)
userId int not null primary key
menuId int not null primary key
foreign key (userId) references Users(userId)
foreign key (menuId) references SystemMenu (menuId)
－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－
The Record Of Users (omit)：
userId
1

The Record Of SystemMenu (omit)：
menuId
1
2
3
4
5
6

The Record Of user_menu (omit)：
userId menuId
1 1
1 2
1 3
1 4
1 5
1 6
－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－
public class
{
private Integer userId;
private Set systemMenus = new TreeSet();
...
}

public class SystemMenu
{
private Integer menuId;
...
}
－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－
User.hbm.xml
<hibernate-mapping>
<class name="User" table="Users">
<id name="userId" type="integer" column="userId">
<generator class="native" />
</id>
...
<set name="systemMenus" table="user_menu" lazy="false" inverse="false" order-by="menuId" sort="natural">
<key column="userId" />
<many-to-many column="menuId"class="SystemMenu" />
</set>
</class>
</hibernate-mapping>

SystemMenu.hbm.xml
<hibernate-mapping>
<class name="SystemMenu" table="SystemMenu">
<id name="userId" type="integer" column="userId">
<generator class="native" />
</id>
...
</class>
</hibernate-mapping>
－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－
requirement:
given a user,then get it's systemMenus,but the systemMenus must be sorted,the order must be according to the primary key of the table.
On the jsp page,I want to output the data by use iterator,it may like this:

SystemMenu parentMenu=null;
Collection data=(Collection)request.getAttribute("data");
Iterator parentIt=(Iterator)data.iterator();
while(parentIt.hasNext())
{
parentMenu=(SystemMenu)parentIt.next();
out.println(parentMenu.getMenuName());
}

But,where I refresh the jsp page,the result of every time is different.
in order to resolve the problem,I have use the TreeSet,also I defined the sort in User.hbm.xml.
Now,there is some Exception.
－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－
Excepiton:
java.lang.ClassCastException: SystemMenu
at java.util.TreeMap.compare(TreeMap.java:1093)
at java.util.TreeMap.put(TreeMap.java:465)
at java.util.TreeSet.add(TreeSet.java:210)
at java.util.AbstractCollection.addAll(AbstractCollection.java:318)
at java.util.TreeSet.addAll(TreeSet.java:258)
at org.hibernate.collection.PersistentSet.endRead(PersistentSet.java:273)
at org.hibernate.engine.CollectionLoadContext.endLoadingCollection
...
－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－
If I remove " sort='natural' " from "User.hbm.xml" ,then this is no exception,I want to know why and how to resolve this problem.
Thanks for everyone.

Hi!

You tried pretty hard to obfuscate your problem. If you edit the stack-trace before asking for help, you should try not to hide the actual exception. :(
However, I assume that it is a ClassCastException. Objects that are stored in a TreeSet (see http://java.sun.com/j2se/1.4.2/docs/api/java/util/TreeSet.html) (or in a SortedSet in general) have to implement the Comparable interface. You should check the Javadoc on the TreeSet (especially the part concerning "consistency with equals").

All the best,

René

Dear ReneStolp：
Thank you very much.
I am a chinese,my englist is not very good,so there may be some mistake in my post.
I have edit the exception.The exception is ClassCastException.Your assume is correct.
I also edit the java class:SystemMenu

public class SystemMenu implements Comparator
{
private Integer menuId;

public int compare(Object o1, Object o2)
{
SystemMenu sm1 = (SystemMenu) o1;
SystemMenu sm2 = (SystemMenu) o2;
return sm1.getMenuId().intValue() - sm2.getMenuId().intValue();
}

public boolean equals(Object obj)
{
boolean val = false;
SystemMenu sm = (SystemMenu) obj;
if (this.getMenuId().intValue() == sm.getMenuId().intValue())
{
val = true;
}
return val;
}
...
}

But,there is still some error in my program:
java.lang.ClassCastException:SystemMenu

Uops! Implements Comparable instead Comparator.

valeuz...

Dear Marcos Silva Pereira:
Thank you very much.
I have edit my program.
There is no exception.
But the data is not sorted.

public class SystemMenu implements Comparable
{
private Integer menuId;
public int compareTo(Object obj)
{
SystemMenu sm = (SystemMenu) obj;
return this.getMenuId().intValue() - sm.getMenuId().intValue();
}
...
}

Thank's for every one.
I have resolve my problem.

Hi!



Glad to hear that. You may want to rate the responses if they helped (see http://forum.hibernate.org/credits.html).

All the best,

René

Please, share with us how do you solve the problem. ;-)

Kind Regads,