Don't merge - Review: Use database where possible for what it's good at

.gitignore

@@ -1,3 +1,3 @@
 bin/rspec
 coverage/
-log/test.log
+log

app/models/answer.rb

@@ -1,30 +1,16 @@
 class Answer < ActiveRecord::Base
+  include Voting
 
   has_many :comments, :as => :commentable
   has_many :votes, :as => :votable
   belongs_to :user
   belongs_to :question
 
   def self.newest_answers
-
-    Answer.order(:updated_at).reverse.group_by{|answer| answer.question_id}.map{|group| group[1][0]}
-
+    where('answers.updated_at = (select max(updated_at) from answers a where a.question_id = answers.question_id)')
   end
 
   def self.top_voted_answer(question)
-    top = question.answers.select{|answer| answer.count_votes.is_a?(Integer)}.sort{|answer| answer.count_votes}.reverse
-    question.answers.each do |answer|
-      if top.exclude?(answer)
-        top << answer
-      end
-    end
-    if top.delete_if{|answer| answer.id == question.accepted_answer_id}
-      top.unshift(question.answers.select{|answer| answer.id == question.accepted_answer_id}.first)
-    end
-    top.compact
-  end
-
-  def count_votes
-    votes.map{|vote| vote.value}.reduce(:+)
+    joins(:votes).where(question:question).group('answers.id').order('sum(votes.value) desc').first
   end
 end

app/models/comment.rb

@@ -1,11 +1,6 @@
 class Comment < ActiveRecord::Base
-
+  include Voting
   has_many :votes, :as => :votable
   belongs_to :user
   belongs_to :commentable, polymorphic: true
-
-
-  def count_votes
-    votes.map{|vote| vote.value}.reduce(:+)
-  end
 end

app/models/concerns/voting.rb

@@ -0,0 +1,5 @@
+module Voting
+  def count_votes
+    votes.sum(:value)
+  end
+end

app/models/question.rb

@@ -1,37 +1,40 @@
 class Question < ActiveRecord::Base
+  include Voting
   belongs_to :user
   has_many :answers
   has_many :comments, :as => :commentable
   has_many :votes, :as => :votable
 
   def find_accepted_answer
-    self.answers.find(accepted_answer_id)
+    #maybe return nil rather than throwing error here
+    self.answers.find_by(id: accepted_answer_id)
   end
 
   def self.most_recent_questions
-    self.order(:created_at).reverse
+    self.order(created_at: :desc).reverse
   end
 
-  def self.trending_questions
-    Answer.newest_answers.map{|answer| answer.question}
+  def self.trending_questions(limit=20)
+    joins(:answers)
+    .where('answers.created_at = (select max(created_at) from answers where question_id = questions.id)')
+    .order('answers.created_at desc')
+    .limit(limit)
   end
 
   def self.top_voted_questions
-    Question.questions_sorted_by_most_votes + Question.questions_with_no_votes
-  end
-
-  def count_votes
-    votes.map{|vote| vote.value}.reduce(:+)
+    joins("left join votes on votes.votable_id = questions.id \
+            and votes.votable_type = 'Question'")
+    .group('questions.id').order('sum(votes.value) desc')
   end
 
   private
 
   def self.questions_sorted_by_most_votes
-    all.select{|question| question.count_votes.is_a?(Integer)}.sort_by{|question| question.count_votes}.reverse
+    joins(:votes).group('questions.id').order('count(votes.votable_id) desc')
   end
 
   def self.questions_with_no_votes
-    all.select{|question| question.count_votes == nil}
+    includes(:votes).where(votes: { :id => nil })
   end
 
 end

app/models/user.rb

@@ -14,11 +14,11 @@ def password_confirmation_matches
     end
   end
 
+  # This should probably be count_votes and covered by the voting module
+  # I can't see that you call this one anywhere
   def vote_count
-    votes_for.map{|vote| vote.value}.reduce(:+)
+    votes.sum(:value)
   end
 
-
-
   has_secure_password
 end