FIX: Update category tag stats with new or deleted (#21531)

The old method updated only existing records, without considering that
new tags might have been created or some tags might not exist anymore.
This was usually not a problem because the stats were also updated by
other code paths.

However, the ensure consistency job should be more solid and help when
other code paths fail or after importing data.

Also, update category tag stats too should happen when updating other
category stats as well.

app/models/category_tag_stat.rb

@@ -44,23 +44,38 @@ class CategoryTagStat < ActiveRecord::Base
 
   # Recalculate all topic counts if they got out of sync
   def self.update_topic_counts
+    # Add new records or update existing records
     DB.exec <<~SQL
-      UPDATE category_tag_stats stats
+      WITH stats AS (
-      SET topic_count = x.topic_count
+        SELECT topics.category_id as category_id,
-      FROM (
-        SELECT COUNT(topics.id) AS topic_count,
                tags.id AS tag_id,
-               topics.category_id as category_id
+               COUNT(topics.id) AS topic_count
         FROM tags
         INNER JOIN topic_tags ON tags.id = topic_tags.tag_id
         INNER JOIN topics ON topics.id = topic_tags.topic_id
                AND topics.deleted_at IS NULL
                AND topics.category_id IS NOT NULL
-        GROUP BY tags.id, topics.category_id
+        GROUP BY topics.category_id, tags.id
-      ) x
+      )
-      WHERE stats.tag_id = x.tag_id
+      INSERT INTO category_tag_stats(category_id, tag_id, topic_count)
-        AND stats.category_id = x.category_id
+      SELECT category_id, tag_id, topic_count FROM stats
-        AND x.topic_count <> stats.topic_count
+      ON CONFLICT (category_id, tag_id) DO
+      UPDATE SET topic_count = EXCLUDED.topic_count
+    SQL
+
+    # Delete old records
+    DB.exec <<~SQL
+      DELETE FROM category_tag_stats
+      WHERE (category_id, tag_id) NOT IN (
+        SELECT topics.category_id as category_id,
+               tags.id AS tag_id
+        FROM tags
+        INNER JOIN topic_tags ON tags.id = topic_tags.tag_id
+        INNER JOIN topics ON topics.id = topic_tags.topic_id
+               AND topics.deleted_at IS NULL
+               AND topics.category_id IS NOT NULL
+        GROUP BY topics.category_id, tags.id
+      )
     SQL
   end
 end

lib/tasks/categories.rake

@@ -24,6 +24,7 @@ task "categories:move_topics", %i[from_category to_category] => [:environment] d
 
     puts "Updating category stats..."
     Category.update_stats
+    CategoryTagStat.update_topic_counts
   end
 
   puts "", "Done!", ""

spec/models/category_tag_stat_spec.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+describe CategoryTagStat do
+  fab!(:category) { Fabricate(:category) }
+  fab!(:tag) { Fabricate(:tag) }
+  fab!(:topic) { Fabricate(:topic, category: category, tags: [tag]) }
+
+  describe "#update_topic_counts" do
+    it "creates new records" do
+      CategoryTagStat.destroy_all
+
+      expect { CategoryTagStat.update_topic_counts }.to change { CategoryTagStat.count }.by(1)
+      category_tag_stat = CategoryTagStat.last
+      expect(category_tag_stat.category_id).to eq(category.id)
+      expect(category_tag_stat.tag_id).to eq(tag.id)
+      expect(category_tag_stat.topic_count).to eq(1)
+    end
+
+    it "updates existing records" do
+      CategoryTagStat.last.update(topic_count: 10)
+
+      expect { CategoryTagStat.update_topic_counts }.not_to change { CategoryTagStat.count }
+      category_tag_stat = CategoryTagStat.last
+      expect(category_tag_stat.category_id).to eq(category.id)
+      expect(category_tag_stat.tag_id).to eq(tag.id)
+      expect(category_tag_stat.topic_count).to eq(1)
+    end
+
+    it "deletes old records" do
+      CategoryTagStat.last.update(tag_id: Fabricate(:tag).id)
+
+      expect { CategoryTagStat.update_topic_counts }.not_to change { CategoryTagStat.count }
+      category_tag_stat = CategoryTagStat.last
+      expect(category_tag_stat.category_id).to eq(category.id)
+      expect(category_tag_stat.tag_id).to eq(tag.id)
+      expect(category_tag_stat.topic_count).to eq(1)
+    end
+  end
+end