problem with @ManyToMany using MapKeyClass

[alice zhu]

Hello, I have a ManyToMany relationship between two tables: Xa_ Name (which represents a person) and WR_Engineering_Group
-------------------
Table. Xa_Name
Xa_Name_Id (int, pk)
Full name (String)
--------------------

---------------------
Table. WR_Engineering_Group
Id (int, pk)
group_name (String)
-----------------------------

However, the joint table has an extra column to indicate if the person is an activate authority of the group as following:
-------------------
Table. WR_Engineering_Group_Authority
Xa_Name_Id (int, pk) Reference Xa_Name.xa_name_Id
group(int, pk) Reference WR_Engineering_Group_Id
active(boolean, extra column)
--------------------

I use the following mapKeyClass method to join the two tables, and wish to use the attribute "active" to map the corresponding list of persons.

 @ManyToMany
    @JoinTable(name = "WR_ENGINERRING_GROUP_AUTHORITY", joinColumns = {
    @JoinColumn(name = "GROUP", referencedColumnName = "ID", nullable = false)}, inverseJoinColumns = {
        @JoinColumn(name = "XA_NAME_ID", referencedColumnName = "XA_NAME_ID", nullable = false)})
    @MapKeyClass(GroupAuthorityStatus.class)
    private Map<GroupAuthorityStatus, XaName> xaNameList;   

The GroupAuthorityStatus Class is just a embeddable class to wrap the extra column "active". The following is the implementation for this class

 /*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package ca.triumf.mis.qms.workrequest.jpa;

import java.io.Serializable;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Embeddable;
import org.eclipse.persistence.annotations.Convert;

/**
 *
 * @author jyzhu
 */
@Embeddable
public class GroupAuthorityStatus implements Serializable {
    private static final long serialVersionUID = 1L;
    @Basic
    @Column(name = "ACTIVE", nullable = false)
    @Convert("booleanCharConverter")
    private boolean active;

    public GroupAuthorityStatus() {
    }

    public GroupAuthorityStatus(boolean status) {
        this.active = status;
    }

    public boolean isActive() {
        return active;
    }

    public void setActive(boolean active) {
        this.active = active;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final GroupAuthorityStatus other = (GroupAuthorityStatus) obj;
        if (this.active != other.active) {
            return false;
        }
        return true;
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 71 * hash + (this.active ? 1 : 0);
        return hash;
    }
    

}   

That is to say, given a group, I wish to map all the active authorities to a GroupAuthorityStatus that represents "True".

Now, it works fine to map the corresponding authorities and to add a new authority.
However, if I add a new active person as authority for a given group, the previously existing active person will be replaced by this new authority. Same problem occurs with adding a new inactive authority. It seems like only one person can be associated with the key(GroupAuthorityStatus). How could I change it to map a list of perons (List<XaName>) to the key(GroupAuthorityStatus).
The following is the method of activating a previously inactive authority. I remove the person first, and then add the person with true for its activity.
This works fine as long as there is only one person associated with the targeting status. If there already exists one person with the same status, the old person gets replaced by this incoming authority.

   public void activate(Entry<GroupAuthorityStatus, XaName> entry){
         authority = entry.getValue();
         engineeringGroup.getXaNameList().entrySet().remove(entry);
         engineeringGroupManager.edit(engineeringGroup);
         engineeringGroup.getXaNameList().put(new GroupAuthorityStatus(true),authority);
         engineeringGroupManager.edit(engineeringGroup);
         engineeringGroupManager.flush();
    }  

Any hint and help is greatly appreciated. Thank you very much for your time in advance.
By the way, I got the format of such mapkeyclass method from the following website:
google book for JPA2
MapKeyColumns from wiki

[Bear Bibeault]

"alice NotInWonderland", please check your private messages for an important administrative matter.

[James Sutherland]

You can't use the active flag as a Map key if it is not unique. You seem to want sub kind of nested collection, i.e. Group - xNames Map<boolean active, List<XName>>.

JPA does not allow that, you can't map nested collections without an intermediate object.
You need to create an object that represents the join table,
i.e.
either,
GroupAuthorityStatusXName is an Entity and maps to the join table, Group has a 1-m to GroupAuthorityStatusXName, GroupAuthorityStatusXName has a m-1 to XName

or,
GroupAuthorityStatusXName is an Embeddable, Group has a ElementCollection to GroupAuthorityStatusXName, GroupAuthorityStatusXName has a m-1 to XName

See,
http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany#Mapping_a_Join_Table_with_Additional_Columns

and,
http://en.wikibooks.org/wiki/Java_Persistence/Relationships#Nested_Collections.2C_Maps_and_Matrices

[alice zhu]

James Sutherland wrote:You can't use the active flag as a Map key if it is not unique. You seem to want sub kind of nested collection, i.e. Group - xNames Map<boolean active, List<XName>>.

JPA does not allow that, you can't map nested collections without an intermediate object.
You need to create an object that represents the join table,
i.e.
either,
GroupAuthorityStatusXName is an Entity and maps to the join table, Group has a 1-m to GroupAuthorityStatusXName, GroupAuthorityStatusXName has a m-1 to XName

or,
GroupAuthorityStatusXName is an Embeddable, Group has a ElementCollection to GroupAuthorityStatusXName, GroupAuthorityStatusXName has a m-1 to XName

See,
http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany#Mapping_a_Join_Table_with_Additional_Columns

and,
http://en.wikibooks.org/wiki/Java_Persistence/Relationships#Nested_Collections.2C_Maps_and_Matrices

Thank you very much, James! I tried it, and it works really well with the JPA. I mean, I used the ElementCollection strategy. I didn't know the nested collection is not supported in JPA. Thanks a lot for your time and suggestion!