Use AR relations when merging comments

Using arrays made it difficult to order by more than one field (like the
`most_voted` scope does), and so we were ordering by `confidence_score`
and ignoring the `created_at` column.

Using an AR relation makes it easy to reuse the existing `most_voted`
scope.

This change has one side effect: now comments with equal votes are
ordered in descending order instead of having no specific order. That
means flaky specs which failed sometimes because they assumed comments
were ordered by date are now always green.

I've also re-added the `oldest` scope removed in 792b15b thinking it was
removed because using it with arrays was too hard.

app/controllers/legislation/annotations_controller.rb

@@ -8,7 +8,7 @@ class Legislation::AnnotationsController < Legislation::BaseController
   load_and_authorize_resource :draft_version, through: :process
   load_and_authorize_resource
 
-  has_orders %w{most_voted newest}, only: :show
+  has_orders %w[most_voted newest oldest], only: :show
 
   def index
     @annotations = @draft_version.annotations

lib/merged_comment_tree.rb

@@ -1,24 +1,13 @@
 class MergedCommentTree < CommentTree
-  attr_reader :commentables, :array_order
+  attr_reader :commentables
 
   def initialize(commentables, page, order = "confidence_score")
     @commentables = commentables
     super(commentables.first, page, order)
-    @array_order = set_array_order(order)
   end
 
-  def root_comments
+  def base_comments
-    Kaminari.paginate_array(commentables.flatten.map(&:comments).map(&:roots).flatten.sort_by {|a| a[array_order]}.reverse).
+    Comment.where(commentable: commentables.flatten)
-    page(page).per(ROOT_COMMENTS_PER_PAGE)
-  end
-
-  def set_array_order(order)
-    case order
-    when "newest"
-      "created_at"
-    else
-      "confidence_score"
-    end
   end
 
 end

spec/features/comments/legislation_annotations_spec.rb

@@ -14,7 +14,7 @@ describe "Commenting legislation questions" do
 
     expect(page).to have_css(".comment", count: 4)
 
-    comment = Comment.first
+    comment = Comment.last
     within first(".comment") do
       expect(page).to have_content comment.user.name
       expect(page).to have_content I18n.l(comment.created_at, format: :datetime)
@@ -144,7 +144,7 @@ describe "Commenting legislation questions" do
                                                             legislation_annotation.draft_version,
                                                             legislation_annotation)
 
-    within all(".comment").last do
+    within all(".comment").first do
       expect(page).to have_content "Built with http://rubyonrails.org/"
       expect(page).to have_link("http://rubyonrails.org/", href: "http://rubyonrails.org/")
       expect(find_link("http://rubyonrails.org/")[:rel]).to eq("nofollow")
@@ -160,7 +160,7 @@ describe "Commenting legislation questions" do
                                                             legislation_annotation.draft_version,
                                                             legislation_annotation)
 
-    within all(".comment").last do
+    within all(".comment").first do
       expect(page).to have_content "click me http://www.url.com"
       expect(page).to have_link("http://www.url.com", href: "http://www.url.com")
       expect(page).not_to have_link("click me")