Mongoid: How can I make Mongoid recognize my custom ActiveModel validations?

I have a model, which has and array of names and I want to ensure that only one document can have a given name. I'm trying to write a custom validation to handle this. My custom validation and the model look like this at the moment:

lib/unique_name_validator.rb

class UniqueNamesValidator < ActiveModel::EachValidator
  def validate_each( record, attribute, value )
  end
end

app/models/MyModel.rb

class MyModel
  include Mongoid::Document

  validates :names, :un开发者_如何学编程ique_names => true

  field :names, :type => Array
end

But I'm getting Unknown validator: 'unique_names' (ArgumentError). The Mongoid documentation says that each model includes ActiveModel::Validation, which I thought would allow them to work with my custom validations. I've also tried making validation that inherits from ActiveModel::Validator and using validates_with, but that doesn't work either.

If you're using Rails 3, your unique_name_validator.rb may not be picked up from under lib automatically unless you add the following in application.rb:

config.autoload_paths += %W(#{config.root}/lib)

The custom validation works for me with mongoid, but I needed to require it from my model file:

require 'unique_name_validator'

Perhaps there is a way to configure rails/mongoid to automatically pick up custom validators?

Either autoload lib file in application.rb

config.autoload_paths += %W(#{config.root}/lib)

Or drop unique_name_validator.rb to initializer folder

For uniqueness, use:

validates_uniqueness_of

(From http://mongoid.org/docs/validation/)

validates_each works too.