AssociationCountValidator

As a result of my previous blog post about validating nested associations, I wrote custom validator for Rails 3. It is intended to help you to validate records count in a given association.

# lib/association_count_validator.rb
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

Probably, you noticed that this is just a wrapper over the standard LengthValidator. This has a big advantage - all options, provided by the basic validator, are supported. And it correctly handles the situation with marked for destruction records, which was mentioned in the previous post.

Usage:

class Company < ActiveRecord::Base
  OFFICES_COUNT_MIN = 1

  attr_accessible :name, :offices_attributes

  validates :name, presence: true
  validates :offices, association_count: { minimum: OFFICES_COUNT_MIN }

  has_many :offices, inverse_of: :company

  accepts_nested_attributes_for :offices, allow_destroy: true
end

Do not forget to add custom error messages to your localization files.

Example for en culture:

en:
  errors:
    messages:
      association_count_less_than_or_equal_to:
        one: count must be less than 1
        other: count must be less than or equal to %{count}
      association_count_greater_than_or_equal_to:
        one: count must be greater than 1
        other: count must be greater than or equal to %{count}
      association_count_invalid:
        one: count is invalid (must be equal to 1)
        other: count is invalid (must be equal to %{count})

Anton Kaliaev

Software engineer, blogger, public speaker, traveler

Ulyanovsk, Russia http://homeonrails.com