Uniqueness validation on mult. attrs. / validation order

Rails
1

All,

  1. Is there any easier way than writing a custom validate() method to
    enforce the uniqueness of more than one attribute?

  2. Given a parent/child relationship between AR classes (i.e. parent
    “has_many” children) - is there any way to enforce that the validation
    for the parent happens first before the validation of the children?

Thanks,
Wes