[web2py] Some help on validation

[JavierQQ]

Hi,

I'm just trying to use again web2py :)
I'm in kind of a trouble (it's not a web2py problem, it's actually a
validation question)
I have a Scale model

db.define_table('scale', Field('name','string'),
                         Field('group_id',db.groups)
                         Field('min_v','integer'),
                         Field('max_v','integer'),
                         Field('category','string'))

and Group model

db.define_table('groups', Field('name','string'))

I want to validate the existance of only 1 scale per group, for
example
Group 1:
- scale 1 :
   ....
   - min_v : 0
   - max_v: 10

- scale 2 :
   ....
   - min_v : 21
   - max_v: 30


So when someone types (for example):
- scale 3:
   - min_v :8
   - max_v: 23

It won't be accepted, Is there a way of doing that?... I think it's
more of a query problem and not a web2py issue,
but I'll really appreciate the help

Thanks in advance

Javier Q.