module Validation
  module ClassMethods
    def validates_uniqueness_of(*atts)
      opts = {
        :message => 'is already taken',
      }.merge!(atts.extract_options!)

      validates_each(*atts) do |o, a, v|
        o.errors[a] << opts[:message] unless v && !v.blank? && !o.class[a => v]
      end
    end
  end
end

class User < Sequel::Model

  validates do
    presence_of :username
    length_of :username, :within => 1..32
    format_of :username, :with => /^\w+$/

    presence_of :password
    length_of :password, :is => 40

    uniqueness_of :email
  end

end