add a rake task to move all topics from one category to another

lib/tasks/categories.rake

@@ -0,0 +1,20 @@
+task "categories:move_topics", [:from_category, :to_category] => [:environment] do |_, args|
+  from_category_id = args[:from_category]
+  to_category_id = args[:to_category]
+
+  if !from_category_id || !to_category_id
+    puts "ERROR: Expecting categories:move_topics[from_category_id,to_category_id]"
+    exit 1
+  end
+
+  from_category = Category.find(from_category_id)
+  to_category = Category.find(to_category_id)
+
+  if from_category && to_category
+    Topic.where(category_id: from_category_id).update_all(category_id: to_category_id)
+    from_category.update_attribute(:topic_count, 0)
+    Category.update_stats
+  end
+
+  puts "", "Done!", ""
+end