/moderator/dashboard: optimize sql queries

* Converts queries to use active record instead of raw sql. This ensures
  that user objects are loaded by rails in the join, so that we
  don't have to issue `User.find` calls to load users one-by-one.

* Use `.includes` to preload associations used in the view, to avoid
  additional N+1 query problems (primarily, calls to link_to_user
  also causing users to be loaded one-by-one).

app/logical/moderator/dashboard/queries/post_appeal.rb

@@ -2,28 +2,13 @@ module Moderator
   module Dashboard
     module Queries
       class PostAppeal
-        attr_reader :post, :count
-
         def self.all(min_date)
-          sql = <<-EOS
-            SELECT post_appeals.post_id, count(*)
-            FROM post_appeals
-            JOIN posts ON posts.id = post_appeals.post_id
-            WHERE
-              post_appeals.created_at > ?
-              and posts.is_deleted = true
-              and posts.is_pending = false
-            GROUP BY post_appeals.post_id
-            ORDER BY count(*) DESC
-            LIMIT 10
-          EOS
-
-          ActiveRecord::Base.select_all_sql(sql, min_date).map {|x| new(x)}
-        end
-
-        def initialize(hash)
-          @post = ::Post.find(hash["post_id"])
-          @count = hash["count"]
+          ::Post.joins(:appeals).includes(:uploader, :flags, appeals: [:creator])
+            .deleted
+            .where("post_appeals.created_at > ?", min_date)
+            .group(:id)
+            .order("count(*) desc")
+            .limit(10)
         end
       end
     end