fix(tag): prevent dupl. tags on concurrent inserts

Author: hinaloe

app/models/tag.rb

@@ -91,7 +91,11 @@ def history
   class << self
     def find_or_create_by_names(name_or_names)
       Array(name_or_names).map(&method(:normalize)).uniq { |str| str.mb_chars.downcase.to_s }.map do |normalized_name|
-        tag = matching_name(normalized_name).first || create(name: normalized_name)
+        tag = begin
+          matching_name(normalized_name).first || create!(name: normalized_name)
+        rescue ActiveRecord::RecordNotUnique
+          find_normalized(normalized_name)
+        end
 
         yield tag if block_given?
 

spec/models/tag_spec.rb

@@ -134,6 +134,27 @@
     end
   end
 
+  describe '.find_or_create_by_names race condition' do
+    it 'handles simultaneous inserts of the same tag in different cases without error' do
+      tag_name_upper = 'Rails'
+      tag_name_lower = 'rails'
+
+      threads = []
+
+      2.times do |i|
+        threads << Thread.new do
+          described_class.find_or_create_by_names(i.zero? ? tag_name_upper : tag_name_lower)
+        end
+      end
+
+      threads.each(&:join)
+
+      tags = described_class.where('lower(name) = ?', tag_name_lower.downcase)
+      expect(tags.count).to eq(1)
+      expect(tags.first.name.downcase).to eq(tag_name_lower.downcase)
+    end
+  end
+
   describe '.search_for' do
     it 'finds tag records with matching names' do
       tag = Fabricate(:tag, name: "match")