ruby
# encoding: utf-8
module Trst
  class Firm
    include Mongoid::Document
    include Mongoid::Timestamps
    include ViewHelpers

    field :name,                type: Array,         default: ['ShortName','FullName','OfficialName']
    field :identities,          type: Hash,          default: {"caen" => "xxx", "chambcom" => "J", "fiscal" => "RO", "account" => "xxx", "itm" => "xxx", "internet" => "xxx.xxx.xxx.xxx", "cod" => "XXX"}
    field :contact,             type: Hash,          default: {"phone" => "xxxx", "fax" => "xxx", "email" => "xx@xxx.xxx", "website" => "xxxx"}
    field :about,               type: Hash,          default: {"scope" => "Scope ...?...", "descript" => "Descript ...?..."}

    validate :identities_fiscal_uniq

    # @todo
    def view_filter
      [id, name[1]]
    end

    protected

    # @todo
    def identities_fiscal_uniq
      return if !identities.key?('fiscal')
      if self.class.where(:'identities.fiscal' => identities['fiscal']) && new_record?
        self.errors.add(:'identities.fiscal', :taken)
      end
    end
  end # Firm
end # Trst

 validates_uniqueness_of :'identities.fiscal',     :case_sensitive => false

f = Trst::Firm.first
 => #<Wstm::PartnerFirm _id: 4e07751d81cb1542ca000001, created_at: 2012-11-04 07:41:01 UTC, updated_at: 2013-01-26 18:28:28 UTC, name: ["Diren", "Diren Exim", "S.C. Diren Exim S.R.L."], identities: {"caen"="xxx", "chambcom"="J12/1000/2000", "fiscal"="RO13354034", "account"="DIR", "itm"="23385-12898/09.04.2004", "internet"="xxx.xxx.xxx.xxx", "cod"="DIR"}, contact: {"phone"="0364-410142", "fax"="0364-410142", "email"="office@diren-reciclare.ro", "website"=>"diren-reciclare.ro"}, about: {"scope"=>"Scope ...?...", "descript"=>"Descript ...?..."}, type: "Wstm::PartnerFirm", client: true, supplr: true, transp: true, p03: false, firm: true, name[1]: "Diren Exim"
ruby-2.1.1 > f.errors.add(:'identities.fiscal',:taken)
NoMethodError: undefined method `identities.fiscal' for #<Wstm::PartnerFirm:0x00000005994f58>
        from /home/kfl62/work/trst_sys_sinatra/.bundle/ruby/2.1.0/gems/mongoid-3.1.6/lib/mongoid/attributes.rb:320:in `method_missing'
        from /home/kfl62/work/trst_sys_sinatra/.bundle/ruby/2.1.0/gems/mongoid-3.1.6/lib/mongoid/validations.rb:66:in `read_attribute_for_validation'
...