FIX: topic and post counts on /categories page should include sub-categories

app/models/category.rb

@@ -44,6 +44,7 @@ class Category < ActiveRecord::Base
 
   has_one :category_search_data
   belongs_to :parent_category, class_name: 'Category'
+  has_many :subcategories, class_name: 'Category', foreign_key: 'parent_category_id'
 
   scope :latest, ->{ order('topic_count desc') }
 

app/serializers/category_detailed_serializer.rb

@@ -17,31 +17,6 @@ class CategoryDetailedSerializer < BasicCategorySerializer
   has_many :featured_users, serializer: BasicUserSerializer
   has_many :displayable_topics, serializer: ListableTopicSerializer, embed: :objects, key: :topics
 
-
-  def topics_week
-    object.topics_week || 0
-  end
-
-  def topics_month
-    object.topics_month || 0
-  end
-
-  def topics_year
-    object.topics_year || 0
-  end
-
-  def posts_week
-    object.posts_week || 0
-  end
-
-  def posts_month
-    object.posts_month || 0
-  end
-
-  def posts_year
-    object.posts_year || 0
-  end
-
   def is_uncategorized
     object.id == SiteSetting.uncategorized_category_id
   end
@@ -62,4 +37,42 @@ class CategoryDetailedSerializer < BasicCategorySerializer
     subcategory_ids.present?
   end
 
+  # Topic and post counts, including counts from the sub-categories:
+
+  def topics_day
+    count_with_subcategories(:topics_day)
+  end
+
+  def topics_week
+    count_with_subcategories(:topics_week)
+  end
+
+  def topics_month
+    count_with_subcategories(:topics_month)
+  end
+
+  def topics_year
+    count_with_subcategories(:topics_year)
+  end
+
+  def posts_day
+    count_with_subcategories(:posts_day)
+  end
+
+  def posts_week
+    count_with_subcategories(:posts_week)
+  end
+
+  def posts_month
+    count_with_subcategories(:posts_month)
+  end
+
+  def posts_year
+    count_with_subcategories(:posts_year)
+  end
+
+  def count_with_subcategories(method)
+    object.subcategories.inject(object.send(method) || 0) { |sum,c| sum += c.send(method) }
+  end
+
 end