Validate groups of attributes

Hi, one of my models has a group of attributes that need to be in a
certain relationship to each other to be valid. So instead of validating
them individually I would like to validate them as a group, and, if
they are not valid, add one and only one error message to model.errors.
How can this be done? Thanks! Ingo

I found the answer. Here it in case this is useful for anybody:

class Rectangle < ActiveRecord::Base
def validate
unless self.left < self.right and < self.bottom
self.errors.add(:bounds, ‘invalid bounds’)

what I didn’t know if that if an ActiveRecord model implements
‘validate’, that method is invoked on validation.