[ACCEPTED]-How do I validate members of an array field?-mongoid

You can define custom ArrayValidator. Place following 3 in app/validators/array_validator.rb:

class ArrayValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, values)
    Array(values).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

You can use it like this in your models:

class User
  include Mongoid::Document
  field :tags, Array

  validates :tags, array: { presence: true, inclusion: { in: %w{ ruby rails } }
end

It 2 will validate each element from the array against 1 every validator specified within array hash.

Milovan's answer got an upvote from me but 13 the implementation has a few problems:

1. Flattening 12 nested arrays changes behavior and hides 11 invalid values.

2. nil field values are treated 10 as [nil], which doesn't seem right.

3. The provided 9 example, with presence: true will generate a NotImplementedError error because 8 PresenceValidator does not implement validate_each.

4. Instantiating a new 7 validator instance for every value in the 6 array on every validation is rather inefficient.

5. The 5 generated error messages do not show why 4 element of the array is invalid, which creates 3 a poor user experience.

Here is an updated 2 enumerable and array validator that addresses all these issues. The code 1 is included below for convenience.

# 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]
        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

You'll probably want to define your own 5 custom validator for the emails field.

So 4 you'll add after your class definition,

validate :validate_emails

def validate_emails
  invalid_emails = self.emails.map{ |email| email.match(/^([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})$/i) }.select{ |e| e != nil }
  errors.add(:emails, 'invalid email address') unless invalid_emails.empty?
end

The 3 regex itself may not be perfect, but this 2 is the basic idea. You can check out the 1 rails guide as follows:

http://guides.rubyonrails.org/v2.3.8/activerecord_validations_callbacks.html#creating-custom-validation-methods

Found myself trying to solve this problem 5 just now. I've modified Tim O's answer slightly 4 to come up with the following, which provides 3 cleaner output and more information to the 2 errors object that you can then display 1 to the user in the view.

validate :validate_emails

def validate_emails
  emails.each do |email|
    unless email.match(/^([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})$/i)
      errors.add(:emails, "#{email} is not a valid email address.")
    end
  end
end