models

class Supplier < ActiveRecord::Base

  validates :country, :inclusion => { :in => Currency.countries,
    :message => "Country can only be #{Currency.countries.join(', ')}"}
end

class Currency < ActiveRecord::Base
	def self.countries
		pluck :country
	end
end

running specs

 ~/development/supplier_app $ bundle exec rspec spec/models
.
Finished in 0.11605 seconds
1 example, 0 failures
 ~/development/supplier_app $ bundle exec rspec spec
F.
Failures:
  1) Supplier Validations: Country needs to be in list of Currencies
     Failure/Error: good_country_supplier.should be_valid
       expected valid? to return true, got false
     # ./spec/models/supplier_spec.rb:49
Finished in 0.678 seconds
2 examples, 1 failure
Failed examples:
rspec ./spec/models/supplier_spec.rb:37 # Supplier Validations: Country needs to be in list of Currencies

spec

    its "Country needs to be in list of Currencies" do
      Currency.create(:country=>"US",:currency=>"USD")
      good_country_supplier = Supplier.new(:country => "US")
  
      good_country_supplier.should be_valid
    end

Test Console

 ~/development/supplier_app $ rails c test
Loading test environment (Rails 3.2.1)
irb(main):001:0> Currency.pluck :country
   (0.3ms)  SELECT country FROM "currencies"
=> ["US"]
irb(main):002:0> s = Supplier.new(:country => "US")
=> #<Supplier id: nil, company: nil, purchasing_org: "A001", account_group: "0001", name: nil, search_term_1: nil, count
ry: "US", language: "E", tax_number_1: "SSN for US OR GST for CA", tax_number_2: "EIN for US OR HST for CA", tax_type: n
il, vat: nil, tax_number: "QST for CA", bank_country: nil, bank_key: nil, bank_account: nil, bank_account_holder: nil, b
ank_type: "BNK1", recon_account: "200010", payment_terms: nil, check_double_inv: "X", payment_methods: nil, wh_tax_count
ry: nil, wh_tax_type: nil, wh_tax_code: nil, liable: nil, rec_type: nil, exemption_number: nil, exemption_pct: nil, exem
ption_reason: nil, exemption_from: nil, exemption_to: nil, order_currency: nil, terms_of_payment: nil, incoterms: nil, i
ncoterms_2: nil, abc_indicator: nil, created_at: nil, updated_at: nil, good_or_service: nil, payee_type: nil, location_s
ervice_performed: nil>
irb(main):003:0> s.valid?
=> true
irb(main):004:0>