validates :author_id, :presence => true, :numericality => true, :existence => {:both => false}
validates :t, :presence => true, :numericality => {:greater_than_or_equal_to => 0}
validates :author_id, :presence => true, :numericality => true, :existence => {:both => false}
validates :t, :presence => true, :numericality => {:greater_than_or_equal_to => 0}