Question

In my rails app I have 2 models: post and post_translations.

class PostTranslation < ActiveRecord::Base
  belongs_to :post

  LANGUAGES = %w( en fr es de it )
  validates_inclusion_of :language, :in => LANGUAGES

end

class Post < ActiveRecord::Base
  has_many :post_translations

end

I want to prevent the same language translation from being submitted twice, so I want to limit the enums to the values not listed in the language column of a particular post_id.
I don’t know if I should do this in model, controller or helper.
Which is the best practice?

Thanks in advance.

Answer 1

I’d use an attribute on the class instead of defining it on an instance.

class PostTranslation < ActiveRecord::Base
  @@languages = %w( en fr es de it )
  cattr_reader :languages

  belongs_to :post

  validates :language, :inclusion => { :in => @@languages },
    :uniqueness => { :scope => :post_id }
end

Now to fulfill your requirement of showing only the languages without translations, define a method on Post:

class Post < ActiveRecord::Base
  has_many :post_translations

  def untranslated
    PostTranslation.languages - post_translations.map(&:language)
  end
end

Then you can build a select menu by getting a post (@post = Post.find(params[:id]) and populating the collection from @post.untranslated.