Add filter to recent topics

app/models/topic.rb

@@ -42,14 +42,21 @@ class Topic < ActiveRecord::Base
   acts_as_readable
 
   def self.recent_topics
-    Post.joins("LEFT OUTER JOIN topics ON topics.id = posts.topic_id").
-      joins("LEFT OUTER JOIN forums on forums.id = topics.forum_id").
-      joins("LEFT OUTER JOIN forumers on forums.id = forumers.forum_id").
-      order("posts.id desc").
-      where("forumers.id IS NULL").
-      select("DISTINCT topic_id").
-      limit(5).
-      map(&:topic)
+    self.find_by_sql %q{
+      SELECT DISTINCT topics.* 
+        FROM  (SELECT id, topic_id
+                FROM   posts 
+                ORDER  BY id DESC 
+                LIMIT  20) AS T 
+               INNER JOIN topics 
+                       ON T.topic_id = topics.id 
+               INNER JOIN forums 
+                       ON forums.id = topics.forum_id 
+               LEFT OUTER JOIN forumers 
+                            ON forumers.forum_id = forums.id 
+        WHERE forumers.id IS NULL 
+        LIMIT  5 
+    }
   end
 
   def to_s

spec/factories/topic.rb

@@ -1,6 +1,6 @@
 FactoryGirl.define do
   factory :topic do
-    sequence(:title) { |n| "Forum Title #{n}" }
+    sequence(:title) { |n| "Topic Title #{n}" }
     forum
     user
     before(:create) do |topic|

spec/models/topic_spec.rb

@@ -29,16 +29,17 @@ describe Topic do
   end
 
   describe ".recent_topics" do
-    before(:each) do
-      5.times do
+    it "returns 5 unique, most recently posted topics" do
+      topics = []
+      6.times do
         topic = create :topic
+        topics << topic
         3.times { create :post, topic: topic }
       end
-    end
-    it "returns 5 unique, most recently posted topics" do
       recent_topics = Topic.recent_topics
-      expect(recent_topics.length).to eq(5)
-      expect(recent_topics.map(&:id).uniq.length).to eq(5)
+      topics.last(5).each do |topic|
+        expect(recent_topics).to include(topic)
+      end
     end
     it "does not return posts from restricted forums" do
       restricted_topic = create :topic, title: "Restricted"