Rails: limit enum column for already submitted values -

in rails app have 2 models: post , post_translations.

class posttranslation < activerecord::base   belongs_to :post    languages = %w( en fr es de )   validates_inclusion_of :language, :in => languages  end  class post < activerecord::base   has_many :post_translations  end 

i want prevent same language translation being submitted twice, want limit enums values not listed in language column of particular post_id.
don't know if should in model, controller or helper.
best practice?

thanks in advance.

i'd use attribute on class instead of defining on instance.

class posttranslation < activerecord::base   @@languages = %w( en fr es de )   cattr_reader :languages    belongs_to :post    validates :language, :inclusion => { :in => @@languages },     :uniqueness => { :scope => :post_id } end 

now fulfill requirement of showing languages without translations, define method on post:

class post < activerecord::base   has_many :post_translations    def untranslated     posttranslation.languages - post_translations.map(&:language)   end end 

then can build select menu getting post (@post = post.find(params[:id]) , populating collection @post.untranslated.