Fix remove code from promotions migration

core/db/migrate/20190106184413_remove_code_from_spree_promotions.rb

@@ -5,10 +5,11 @@
 class RemoveCodeFromSpreePromotions < ActiveRecord::Migration[5.1]
   class Promotion < ActiveRecord::Base
     self.table_name = "spree_promotions"
+    self.ignored_columns = %w(type)
   end
 
   def up
-    promotions_with_code = Promotion.where.not(code: nil)
+    promotions_with_code = Promotion.where.not(code: [nil, ''])
 
     if promotions_with_code.any?
       # You have some promotions with "code" field present! This is not good

core/spec/migrate/20190106184413_remove_code_from_spree_promotions_spec.rb

@@ -44,7 +44,18 @@
     DatabaseCleaner.clean_with(:truncation)
   end
 
+  let(:promotion_with_code) { create(:promotion) }
+
+  before do
+    # We can't set code via factory since `code=` is currently raising
+    # an error, see more at:
+    # https://github.com/solidusio/solidus/blob/cf96b03eb9e80002b69736e082fd485c870ab5d9/core/app/models/spree/promotion.rb#L65
+    promotion_with_code.update_column(:code, code)
+  end
+
   context 'when there are no promotions with code' do
+    let(:code) { '' }
+
     it 'does not call any promotion with code handler' do
       expect(described_class).not_to receive(:promotions_with_code_handler)
 
@@ -53,14 +64,7 @@
   end
 
   context 'when there are promotions with code' do
-    let(:promotion_with_code) { create(:promotion) }
-
-    before do
-      # We can't set code via factory since `code=` is currently raising
-      # an error, see more at:
-      # https://github.com/solidusio/solidus/blob/cf96b03eb9e80002b69736e082fd485c870ab5d9/core/app/models/spree/promotion.rb#L65
-      promotion_with_code.update_column(:code, 'Just An Old Promo Code')
-    end
+    let(:code) { 'Just An Old Promo Code' }
 
     context 'with the deafult handler (Solidus::Migrations::PromotionWithCodeHandlers::RaiseException)' do
       it 'raise a StandardError exception' do
@@ -96,6 +100,14 @@
           end
         end
 
+        context 'with promotions with type set (legacy feature)' do
+          let(:promotion_with_code) { create(:promotion, type: 'Spree::Promotion') }
+
+          it 'does not raise a STI error' do
+            expect { subject }.not_to raise_error
+          end
+        end
+
         context 'when there is a Spree::PromotionCode with the same value' do
           context 'associated with the same promotion' do
             let!(:existing_promotion_code) { create(:promotion_code, value: 'just an old promo code', promotion: promotion_with_code) }