FIX: Don't select columns if we don't have to.

app/controllers/post_actions_controller.rb

@@ -28,25 +28,9 @@ class PostActionsController < ApplicationController
   def users
     guardian.ensure_can_see_post_actors!(@post.topic, @post_action_type_id)
 
-    users = User.select(['null as post_url',
-                         'users.id',
-                         'users.username',
-                         'users.username_lower',
-                         'users.email',
-                         'users.use_uploaded_avatar',
-                         'users.uploaded_avatar_id',
-                         'users.uploaded_avatar_template',
-                         'post_actions.related_post_id'])
-                .joins(:post_actions)
-                .where(['post_actions.post_id = ? and post_actions.post_action_type_id = ? and post_actions.deleted_at IS NULL', @post.id, @post_action_type_id])
-                .to_a
+    post_actions = @post.post_actions.where(post_action_type_id: @post_action_type_id).includes(:user)
 
-    urls = Post.urls(users.map{|u| u.related_post_id})
-    users.each do |u|
-      u.post_url = urls[u.related_post_id.to_i]
-    end
-
-    render_serialized(users, PostActionUserSerializer)
+    render_serialized(post_actions.to_a, PostActionUserSerializer)
   end
 
   def destroy

app/serializers/post_action_user_serializer.rb

@@ -1,8 +1,20 @@
 class PostActionUserSerializer < BasicUserSerializer
-  attributes :post_url
+  attributes :id, :username, :avatar_template, :post_url
 
-  # reserved
-  def post_url
-    object.post_url
+  def id
+    object.user.id
   end
+
+  def username
+    object.user.username
+  end
+
+  def avatar_template
+    object.user.avatar_template
+  end
+
+  def post_url
+    object.related_post_id
+  end
+
 end