Many-to-many relationship with date dependency

Question

Hi.
We have an application which manages membership of users in groups.
It is typical many-to-many relationship (table users and groups and
relational table usersgroups). So far so good.
But we would like to introduce another condition into this relationship
- date validity.
For example - person should belong to group only from date1 to date2.
I think that relational table should contain not only a couple of id's but also
a two dates (from-to) and all those four together should form primary key.
Then we should need a condition (where) for such relationsphip.
But toplink many-to-many mapping doesn't have any features for this.
Have you any idea how to implement our requirement in another way?
Thanks.

Answer 1

Hello,
I am not sure how you plan on setting those dates for each object in the ManyToMany collection.
The only way I can think of is to treat the usergroup table as its own entity, as a wrapper over groups (or users) in the many to many collection, allowing the application to set the date values directly. This usergroup entity would have a 1:1 to both user and group, while user and/or group would have 1:M to usergroup.
Best Regards,
Chris