Enumerable and array validators for ActiveModel::Validations in Rails. Especially useful with document-oriented databases such as MongoDB (accessed via an ODM framework such as Mongoid).

array_validator.rb

# Syntax sugar
class ArrayValidator < EnumValidator
end

enum_validator.rb

# Validates the values of an Enumerable with other validators.
# Generates error messages that include the index and value of
# invalid elements.
#
# Example:
#
#   validates :values, enum: { presence: true, inclusion: { in: %w{ big small } } }
#
class EnumValidator < ActiveModel::EachValidator

  def initialize(options)
    super
    @validators = options.map do |(key, args)|
      create_validator(key, args)
    end
  end

  def validate_each(record, attribute, values)
    helper = Helper.new(@validators, record, attribute)
    Array.wrap(values).each do |value|
      helper.validate(value)
    end
  end

  private

  class Helper

    def initialize(validators, record, attribute)
      @validators = validators
      @record = record
      @attribute = attribute
      @count = -1
    end

    def validate(value)
      @count += 1
      @validators.each do |validator|
        next if value.nil? && validator.options[:allow_nil]
        next if value.blank? && validator.options[:allow_blank]
        validate_with(validator, value)
      end
    end

    def validate_with(validator, value)
      before_errors = error_count
      run_validator(validator, value)
      if error_count > before_errors
        prefix = "element #{@count} (#{value}) "
        (before_errors...error_count).each do |pos|
          error_messages[pos] = prefix + (error_messages[pos] || 'is invalid')
        end
      end
    end

    def run_validator(validator, value)
      validator.validate_each(@record, @attribute, value)
    rescue NotImplementedError
      validator.validate(@record)
    end

    def error_messages
      @record.errors.messages[@attribute]
    end

    def error_count
      error_messages ? error_messages.length : 0
    end
  end

  def create_validator(key, args)
    opts = {attributes: attributes}
    opts.merge!(args) if args.kind_of?(Hash)
    validator_class(key).new(opts).tap do |validator|
      validator.check_validity!
    end
  end

  def validator_class(key)
    validator_class_name = "#{key.to_s.camelize}Validator"
    validator_class_name.constantize
  rescue NameError
    "ActiveModel::Validations::#{validator_class_name}".constantize
  end
end

In Rails 4.1, the options now include a new :class key (https://github.com/rails/rails/blob/7d84c3a2f7ede0e8d04540e9c0640de7378e9b3a/activemodel/lib/active_model/validator.rb#L85-94), so this will break with this error: uninitialized constant ActiveModel::Validations::ClassValidator.

To fix, remove that key from the options in the initialize method:

def initialize(options)
  super
  @validators = options.except(:class).map do |(key, args)|
    create_validator(key, args)
  end
end

using it like that:
validates :artforms, enum: { format: { with: /\A[A-Z 0-9a-z-\u00C0-\u017F]+\z/ } }, allow_blank: true

I get
ArgumentError (The provided regular expression is using multiline anchors (^ or $), which may present a security risk. Did you mean to use \A and \z, or forgot to add the :multiline => true option?):
app/validators/enum_validator.rb:74:in new' app/validators/enum_validator.rb:74:increate_validator'
app/validators/enum_validator.rb:14:in block in initialize' app/validators/enum_validator.rb:13:ineach'
app/validators/enum_validator.rb:13:in map' app/validators/enum_validator.rb:13:ininitialize'
app/models/artwork.rb:51:in <class:Artwork>' app/models/artwork.rb:1:in<top (required)>'
app/controllers/api/v1/artworks_controller.rb:32:in `index'

I must say I don't really understand your gist right now tough, can you help me?

Thx @monfresh! This solves the problem on rails >= 4.1

Using the validator with ":on" or ":if" fails!!! Any idea?

Here an example:

validates :color, presence: true, array: { inclusion: { in: ['red', 'green'] } }, on: :update, if: :some_method

This code works for me without using :if and :on (Rails >= 4.1):

class ArrayValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, values)
    [values].flatten.each do |value|
      options.each do |key, args|
        validator_options = { attributes: attribute }
        validator_options.merge!(args) if args.is_a?(Hash)

        next if value.nil? && validator_options[:allow_nil]
        next if value.blank? && validator_options[:allow_blank]

        validator_class_name = "#{key.to_s.camelize}Validator"
        validator_class = begin
          validator_class_name.constantize
        rescue NameError
          "ActiveModel::Validations::#{validator_class_name}".constantize
        end

        validator = validator_class.new(validator_options)
        validator.validate_each(record, attribute, value)
      end
    end
  end
end

using:

validates :color, presence: true, array: { inclusion: { in: ['red', 'green'] } } #, on: :update, if: :some_method

# or

validates :color, array: { presence: true, inclusion: { in: ['red', 'green'] } } #, on: :update, if: :some_method 

Rails (4.1.7) slices default keys from options: https://github.com/rails/rails/blob/44e6d91a07c26cfd7d7b5360cc9a8184b0692859/activemodel/lib/active_model/validations/validates.rb#L106

class ArrayValidator < ActiveModel::EachValidator

  def validate_each(record, attribute, values)
    [values].flatten.each do |value|
      options.except(:if, :unless, :on, :strict).each do |key, args|
        validator_options = { attributes: attribute }
        validator_options.merge!(args) if args.is_a?(Hash)

        next if value.nil? && validator_options[:allow_nil]
        next if value.blank? && validator_options[:allow_blank]

        validator_class_name = "#{key.to_s.camelize}Validator"
        validator_class = begin
          validator_class_name.constantize
        rescue NameError
          "ActiveModel::Validations::#{validator_class_name}".constantize
        end

        validator = validator_class.new(validator_options)
        validator.validate_each(record, attribute, value)
      end
    end
  end

end

And here the code for this gist:

def initialize(options)
    super
    @validators = options.except(:class, :if, :unless, :on, :strict).map do |(key, args)|
      create_validator(key, args)
    end
end