AssociationCountValidator

Validador Rails3 personalizado para validar a contagem de registros na associação.

class AssociationCountValidator < ActiveModel::Validations::LengthValidator
  MESSAGES = { :wrong_length => :association_count_invalid,
           :too_short => :association_count_greater_than_or_equal_to,
           :too_long => :association_count_less_than_or_equal_to }.freeze

  def initialize(options)
    MESSAGES.each { |key, message| options[key] ||= message }
    super
  end

  def validate_each(record, attribute, value)
    existing_records = record.send(attribute).reject(&:marked_for_destruction?)
    super(record, attribute, existing_records)
  end
end

Mais sobre o problema ( http://homeonrails.com/2012/10/validating-nested-associations-in-rails/ ) e este validador ( http://homeonrails.com/2012/10/associationcountvalidator/ ).