raltation and inserts

[David Nielsen]

Hi,

I have 2 classes:

Account
   private int id;
   private String username;
   private String password;
   private Collection groups;

Group
   private int id;
   private String name;

the db has 3 tables;

ACCOUNT
GROUP
ACCOUNT_GROUP_REF

where ACCOUNT_GROUP_REF is a join table for my relations,
with 2 collumns:
ACCOUNT_ID
GROUP_ID

Now my question is how do i keep my ACCOUNT_GROUP_REF updated,

the Developer guide describes how to setup selects only,
but what about insert and updates, of the relations ??

Regards,
David Nielsen