#287

backend/app/models/tag.rb

@@ -148,25 +148,23 @@ class Tag < ApplicationRecord
     target_tag => Tag
 
     Tag.transaction do
-      Array(source_tags).compact.uniq.each do |st|
-        st => Tag
+      Array(source_tags).compact.uniq.each do |source_tag|
+        source_tag => Tag
 
-        next if st == target_tag
+        next if source_tag == target_tag
 
-        st.post_tags.find_each do |pt|
-          if PostTag.kept.exists?(post_id: pt.post_id, tag_id: target_tag.id)
-            pt.discard_by!(nil)
-            # discard 後の update! は禁止なので DB を直に更新
-            pt.update_columns(tag_id: target_tag.id, updated_at: Time.current)
-          else
-            pt.update!(tag: target_tag)
+        source_tag.post_tags.kept.find_each do |source_pt|
+          post_id = source_pt.post_id
+          source_pt.discard_by!(nil)
+          unless PostTag.kept.exists?(post_id:, tag: target_tag)
+            PostTag.create!(post_id:, tag: target_tag)
           end
         end
 
-        tag_name = st.tag_name
-        st.discard!
-        tag_name.reload
-        tag_name.update!(canonical: target_tag.tag_name)
+        source_tag_name = source_tag.tag_name
+        source_tag.discard!
+        source_tag_name.reload
+        source_tag_name.update!(canonical: target_tag.tag_name)
       end
 
       # 投稿件数を再集計