수정: Channel 모델 역시 Country 에 의존성을 가집니다.

app/models/channel.rb

@@ -1,4 +1,4 @@
-class Channel < ApplicationRecord
+class Channel < NationRecord
   has_many :order_infos
   has_many :product_options
 

app/models/concerns/parse_country_code.rb

@@ -1,3 +1,9 @@
 module ParseCountryCode
-  attr_accessor :country_code
+  def country_code
+    @country_code ||= 'th'
+  end
+
+  def country_code=(code)
+    @country_code = (code || 'th').downcase
+  end
 end

app/models/country.rb

@@ -3,13 +3,17 @@ class Country < ApplicationRecord
   has_many :products
 
   validates_presence_of :name, :name_ko, :locale, :short_name
+  alias_attribute :code, :short_name
+
+  TH = find_by(short_name: :th)
+  VN = find_by(short_name: :vn)
 
   def self.th
-    find_by(short_name: 'th')
+    TH
   end
 
   def self.vn
-    find_by(short_name: 'vn')
+    VN
   end
 
   def self.undef

app/models/nation_record.rb

@@ -3,12 +3,13 @@ class NationRecord < ApplicationRecord
 
   belongs_to :country, optional: true
 
-  default_scope -> { send(country_code.to_sym) }
+  default_scope -> { send(country_code) }
   scope :th, -> { unscoped.includes(:country).where(country: Country.th) }
   scope :vn, -> { unscoped.includes(:country).where(country: Country.vn) }
   scope :undef, -> { unscoped.includes(:country).where(country: Country.undef) }
   scope :at, ->(key) { unscoped.includes(:country).where(country: Country.at(key)) }
 
+  after_initialize :callback_set_default_country
   before_save :callback_attaching_country
 
   def self.migrate_original_record_to_thai_record
@@ -17,7 +18,15 @@ def self.migrate_original_record_to_thai_record
 
   private
 
+  def callback_set_default_country
+    self.country_id ||= default_country.id
+  end
+
   def callback_attaching_country
-    self.country ||= Country.send(ENV['APP_COUNTRY'])
+    callback_set_default_country
+  end
+
+  def default_country
+    @default_country ||= Country.send(self.class.country_code)
   end
 end

app/services/al_is_well/migrate_for_adapting_country_system.rb

@@ -5,6 +5,7 @@ def self.call
         Country.migrate_input_seed_data
 
         national_models = [
+          Channel,
           OrderInfo,
           Brand,
           Adjustment,

db/migrate/channel/20200308091320_add_country_to_channel.rb

@@ -0,0 +1,5 @@
+class AddCountryToChannel < ActiveRecord::Migration[6.0]
+  def change
+    add_reference :channels, :country, foreign_key: true
+  end
+end