ActiveRecord::Validations::ClassMethods

class Person < ActiveRecord::Base
    validates_presence_of :first_name, :last_name, :login, :email
    validates_format_of :email, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i
    validates_inclusion_of :funkce, :in => %w[THP VL OZ S P]
    validates_uniqueness_of :login

    private

    def validate
        errors.ass(:person, " can't be root.") if self.login == 'root'
    end
end