more improvements for thread list queries

* use Content model (to avoid querying mongo with "$in")
* add indexes for non-default sorts
* streamline api code

api/comment_threads.rb

 get "#{APIPREFIX}/threads" do # retrieve threads by course
   #if a group id is sent, then process the set of threads with that group id or with no group id
+  threads = Content.where(_type:"CommentThread", course_id: params["course_id"])
   if params["group_id"]
-    threads = CommentThread.any_of(
-    {:course_id => params["course_id"],:group_id => params[:group_id]},
-    {:course_id => params["course_id"],:group_id.exists => false},
+    threads = threads.any_of(
+      {:group_id => params[:group_id].to_i},
+      {:group_id.exists => false},
     )
-  else
-    threads = CommentThread.where(course_id: params["course_id"])
-    #else process them all
   end
   handle_threads_query(threads)
 end

api/commentables.rb

@@ -4,13 +4,12 @@ delete "#{APIPREFIX}/:commentable_id/threads" do |commentable_id|
 end
 
 get "#{APIPREFIX}/:commentable_id/threads" do |commentable_id|
+  threads = Content.where(_type:"CommentThread", commentable_id: commentable_id)
   if params["group_id"]
-    threads = CommentThread.any_of(
-    {:commentable_id => commentable_id, :group_id => params[:group_id]}, 
-    {:commentable_id => commentable_id, :group_id.exists => false}, 
+    threads = threads.any_of(
+      {:group_id => params[:group_id].to_i}, 
+      {:group_id.exists => false}, 
     )
-  else
-    threads = commentable.comment_threads
   end
     handle_threads_query(threads)    
 end

models/comment_thread.rb

@@ -24,7 +24,6 @@ class CommentThread < Content
   field :pinned, type: Boolean
 
   index({author_id: 1, course_id: 1})
-  index({_type: 1, course_id: 1, pinned: -1, created_at: -1})
 
   include Tire::Model::Search
   include Tire::Model::Callbacks

models/content.rb

@@ -8,6 +8,10 @@ class Content
   field :historical_abuse_flaggers, type: Array, default: [] #preserve abuse flaggers after a moderator unflags
   field :author_username, type: String, default: nil
   
+  index({_type: 1, course_id: 1, pinned: -1, created_at: -1 }, {background: true} )
+  index({_type: 1, course_id: 1, pinned: -1, comment_count: -1, created_at: -1}, {background: true})
+  index({_type: 1, course_id: 1, pinned: -1, "votes.point" => -1, created_at: -1}, {background: true})
+
   index({comment_thread_id: 1, sk: 1}, {sparse: true})
   index({comment_thread_id: 1, endorsed: 1}, {sparse: true})
 

scripts/db/migrate-004-update-indexes.js

+db.contents.ensureIndex({_type: 1, course_id: 1, pinned: -1, comment_count: -1, created_at: -1}, {background: true})
+db.contents.ensureIndex({_type: 1, course_id: 1, pinned: -1, "votes.point": -1, created_at: -1}, {background: true})

scripts/db/revert-migrate-004-update-indexes.js

+db.contents.dropIndex({_type: 1, course_id: 1, pinned: -1, comment_count: -1, created_at: -1})
+db.contents.dropIndex({_type: 1, course_id: 1, pinned: -1, "votes.point": -1, created_at: -1})