How do I validate members of an array field?

Question

I have this model:

class Campaign

  include Mongoid::Document
  include Mongoid::Timestamps

  field :name, :type => String
  field :subdomain, :type => String
  field :intro, :type => String
  field :body, :type => String
  field :emails, :type => Array
end

Now I want to validate that each email in the emails array is formatted correctly. I read the Mongoid and ActiveModel::Validations documentation but I didn't find how to do this.

Can you show me a pointer?

Answer 1

You can define custom ArrayValidator. Place following 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 will validate each element from the array against every validator specified within array hash.

Answer 2

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

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

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

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

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

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

Here is an updated enumerable and array validator that addresses all these issues. The code 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

Answer 3

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

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

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

Answer 4

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

Answer 5

Here's an example that might help out of the rails api docs: http://apidock.com/rails/ActiveModel/Validations/ClassMethods/validates

The power of the validates method comes when using custom validators and default validators in one call for a given attribute e.g.

class EmailValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    record.errors[attribute] << (options[:message] || "is not an email") unless
      value =~ /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i
  end
end

class Person
  include ActiveModel::Validations
  attr_accessor :name, :email

  validates :name, :presence => true, :uniqueness => true, :length => { :maximum => 100 }
  validates :email, :presence => true, :email => true
end