UniqueNestedValidator

This validator allows you to verify the uniqueness of attributes from nested models.

Add this line to your application's Gemfile:

gem 'unique_nested_validator'

And then execute:

$ bundle

Or install it yourself as:

$ gem install unique_nested_validator

Let's say you have a model for Runner:

class Runner < ActiveRecord::Base
  attr_accessible :email

Then you create a Race and fill in runners using nested forms. In your Race model you will accept nested attributes for the nested model Runner:

class Race < ActiveRecord::Base
  has_many :runners, :dependent => :destroy
  accepts_nested_attributes_for :products

If we want to warrant that there aren't two runners with the same id, so we add the following validation to Race:

  validates :products, :unique_nested => true

Or, if we want to warrant there aren't repeated emails for runners we add the following validation:

  validates :products, :unique_nested => { :with => :email }

And it is possible to set a custom error message:

  validates :products, :unique_nested => { :with => :email, :message => "Two runners cannot have the same email" }

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request