fixes #1680

app/models/forum_post.rb

@@ -8,6 +8,7 @@ class ForumPost < ActiveRecord::Base
   before_validation :initialize_updater
   before_validation :initialize_is_deleted, :on => :create
   after_create :update_topic_updated_at_on_create
+  after_update :update_topic_updated_at_on_update_for_orignal_posts
   after_destroy :update_topic_updated_at_on_destroy
   validates_presence_of :body, :creator_id
   validate :validate_topic_is_unlocked
@@ -95,6 +96,12 @@ class ForumPost < ActiveRecord::Base
     end
   end
 
+  def update_topic_updated_at_on_update_for_orignal_posts
+    if is_original_post?
+      topic.touch
+    end
+  end
+
   def update_topic_updated_at_on_destroy
     max = ForumPost.where(:topic_id => topic.id).maximum(:updated_at)
     if max

test/unit/forum_post_test.rb

@@ -59,13 +59,33 @@ class ForumPostTest < ActiveSupport::TestCase
       end
     end
 
-    should "update its parent when saved" do
+    should "update the topic when created" do
+      @original_topic_updated_at = @topic.updated_at
       Timecop.travel(1.second.from_now) do
-        @original_topic_updated_at = @topic.updated_at
+        post = FactoryGirl.create(:forum_post, :topic_id => @topic.id)
       end
-      post = FactoryGirl.create(:forum_post, :topic_id => @topic.id)
       @topic.reload
-      assert_not_equal(@original_topic_updated_at, @topic.updated_at)
+      assert_not_equal(@original_topic_updated_at.to_s, @topic.updated_at.to_s)
+    end
+
+    should "update the topic when updated only for the original post" do
+      posts = []
+      3.times do
+        posts << FactoryGirl.create(:forum_post, :topic_id => @topic.id, :body => rand(100_000))
+      end
+      
+      # updating the original post
+      Timecop.travel(1.second.from_now) do
+        posts.first.update_attributes(:body => "xxx")
+      end
+      @topic.reload
+      assert_equal(posts.first.updated_at.to_s, @topic.updated_at.to_s)
+
+      # updating a non-original post
+      Timecop.travel(2.seconds.from_now) do
+        posts.last.update_attributes(:body => "xxx")
+      end
+      assert_equal(posts.first.updated_at.to_s, @topic.updated_at.to_s)
     end
 
     should "be searchable by body content" do