Update category's topic_count immediately when trashing or recovering a topic; this ensures that a category can be deleted without waiting for the category_stats job to run.

app/models/topic.rb

@@ -22,11 +22,13 @@ class Topic < ActiveRecord::Base
   versioned if: :new_version_required?
 
   def trash!
+    update_category_topic_count_by(-1) if deleted_at.nil?
     super
     update_flagged_posts_count
   end
 
   def recover!
+    update_category_topic_count_by(1) unless deleted_at.nil?
     super
     update_flagged_posts_count
   end
@@ -630,6 +632,14 @@ class Topic < ActiveRecord::Base
   def secure_category?
     category && category.secure
   end
+
+  private
+
+    def update_category_topic_count_by(num)
+      if category_id.present?
+        Category.where(['id = ?', category_id]).update_all("topic_count = topic_count " + (num > 0 ? '+' : '') + "#{num}")
+      end
+    end
 end
 
 # == Schema Information

spec/models/topic_spec.rb

@@ -1293,4 +1293,36 @@ describe Topic do
       Topic.new(:category => nil).should_not be_secure_category
     end
   end
+
+  describe 'trash!' do
+    context "its category's topic count" do
+      let(:category) { Fabricate(:category) }
+
+      it "subtracts 1 if topic is being deleted" do
+        topic = Fabricate(:topic, category: category)
+        expect { topic.trash! }.to change { category.reload.topic_count }.by(-1)
+      end
+
+      it "doesn't subtract 1 if topic is already deleted" do
+        topic = Fabricate(:topic, category: category, deleted_at: 1.day.ago)
+        expect { topic.trash! }.to_not change { category.reload.topic_count }
+      end
+    end
+  end
+
+  describe 'recover!' do
+    context "its category's topic count" do
+      let(:category) { Fabricate(:category) }
+
+      it "adds 1 if topic is deleted" do
+        topic = Fabricate(:topic, category: category, deleted_at: 1.day.ago)
+        expect { topic.recover! }.to change { category.reload.topic_count }.by(1)
+      end
+
+      it "doesn't add 1 if topic is not deleted" do
+        topic = Fabricate(:topic, category: category)
+        expect { topic.recover! }.to_not change { category.reload.topic_count }
+      end
+    end
+  end
 end