Fix N+1 queries in moderation and fix preload_first_topic_post

app/controllers/thredded/moderation_controller.rb

@@ -19,6 +19,8 @@ def history
       @post_moderation_records = accessible_post_moderation_records
         .order(created_at: :desc)
         .send(Kaminari.config.page_method_name, current_page)
+        .preload(:messageboard, :post_user, :moderator, post: :postable)
+        .preload_first_topic_post
     end
 
     def activity

app/models/concerns/thredded/post_common.rb

@@ -21,13 +21,19 @@ module PostCommon
       scope :preload_first_topic_post, -> {
         posts_table_name = quoted_table_name
         result = all
-        ActiveRecord::Associations::Preloader.new.preload(
-          result.map(&:postable), :first_post,
+        owners_by_id = result.each_with_object({}) { |r, h| h[r.postable_id] = r.postable }
+        preloader = ActiveRecord::Associations::Preloader.new.preload(
+          owners_by_id.values, :first_post,
           unscoped.where(<<~SQL.delete("\n"))
           #{posts_table_name}.created_at = (
           SELECT MAX(p2.created_at) from #{posts_table_name} p2 WHERE p2.postable_id = #{posts_table_name}.postable_id)
         SQL
         )
+        preloader[0].preloaded_records.each do |post|
+          topic = owners_by_id.delete(post.postable_id)
+          next unless topic
+          topic.association(:first_post).target = post
+        end
         result
       }
 

app/models/thredded/post_moderation_record.rb

@@ -27,6 +27,25 @@ class PostModerationRecord < ActiveRecord::Base
       record.errors.add attr, "Post moderation_state is already #{value}" if record.previous_moderation_state == value
     end
 
+    scope :preload_first_topic_post, -> {
+      posts_table_name = Thredded::Post.quoted_table_name
+      result = all
+      owners_by_id = result.each_with_object({}) { |r, h| h[r.post.postable_id] = r.post.postable }
+      preloader = ActiveRecord::Associations::Preloader.new.preload(
+        owners_by_id.values, :first_post,
+        Thredded::Post.unscoped.where(<<~SQL.delete("\n"))
+          #{posts_table_name}.created_at = (
+          SELECT MAX(p2.created_at) from #{posts_table_name} p2 WHERE p2.postable_id = #{posts_table_name}.postable_id)
+      SQL
+      )
+      preloader[0].preloaded_records.each do |post|
+        topic = owners_by_id.delete(post.postable_id)
+        next unless topic
+        topic.association(:first_post).target = post
+      end
+      result
+    }
+
     paginates_per Thredded.posts_per_page
 
     # @return [ActiveRecord::Relation<Thredded.user_class>] users that can read the moderated post.

app/views/thredded/moderation/_post_moderation_record.html.erb

@@ -38,7 +38,8 @@
       <% end %>
     <% end %>
     <% if post %>
-      <%= render 'thredded/posts_common/header_with_user_and_topic', post: post_view, post_user_link: post_user_link %>
+      <%= render 'thredded/posts_common/header_with_user_and_topic',
+                 post: post_view, user: record.post_user, post_user_link: post_user_link %>
     <% else %>
       <header><h2 class="thredded--post--user"><%= post_user_link %></h2></header>
     <% end %>

app/views/thredded/posts_common/_header_with_user_and_topic.html.erb

@@ -1,9 +1,11 @@
 <%# @param post [Thredded::PostView] %>
+<%# @param user [Thredded.user_class] optional %>
 <%# @param post_user_link [String] optional %>
 <% topic = post.to_model.postable %>
-<% post_user_link ||= user_link(post.user) %>
+<% user ||= post.user %>
+<% post_user_link ||= user_link(user) %>
 <header>
-  <%= image_tag post.avatar_url, class: 'thredded--post--avatar' if post.user %>
+  <%= image_tag Thredded.avatar_url.call(user), class: 'thredded--post--avatar' if user %>
   <h2 class="thredded--post--user-and-topic">
     <%=
       topic_link = link_to(topic.title, post.permalink_path)