[web2py] validation in forms, DAL and Database

[puercoespin]

In a db.py:


db.define_table('vendedor',
                Field('auth_user_id', unique=True, default =
auth.user.id),
                Field('direccion'),
                Field('provincia'),
                Field('coordenadas_gps'),
                Field('email', requires=IS_EMPTY_OR(IS_EMAIL()),
default = auth.user.email),
                Field('telefono', 'integer'),
                Field('profesional', 'boolean', default=True))


In the admin app, raises an error when 'auth_user_id'  values is in
database, but not in controller, allowing repeated values in
'auth_user_id':



default.py


def registrovendedor():

form = SQLFORM(db.vendedor)

    if form.accepts(request.vars, session):
        response.flash = T('Registo válido')
    elif form.errors:
        response.flash = T('Atención: Errores en los datos del
formulario')
    else:
        response.flash = T('Por favor, rellene el formulario de
registro')

    return dict(form=form)


what's wrong? It's necessary to validate in all levels (DAL, Form and
Database)? If you validate at low level (I think in database level),
why you must to validate at form level?

Thanks