module ActiveRecord
  module Validations
   module ClassMethods
      def validates_association_of(*attr_names)
        options = { :message => "is not valid", :on => :save}
        options.update(attr_names.pop) if attr_names.last.is_a?(Hash)
        raise ConfigurationError, ":allow_nil is not supported" if options.has_key?(:allow_nil)
        
        attr_names.each do |attr_name|
          reflection = reflect_on_association(attr_name)
          raise ConfigurationError, "validates_association_of only supports 'belongs_to' associations" unless reflection.macro == :belongs_to
        end
        
        validates_each(attr_names, options) do |record, attr_name, value|
          reflection = reflect_on_association(attr_name)
          record.errors.add(reflection.primary_key_name, options[:message]) if value.nil?
        end
      end
    end
  end
end