pools/show: fix N+1 query on pool show page.

Fix a N+1 query when fetching posts to render thumbnails. Also adds
support for the `limit` url param on the posts show page.

app/controllers/pools_controller.rb

@@ -39,7 +39,7 @@ class PoolsController < ApplicationController
 
   def show
     @pool = Pool.find(params[:id])
-    @post_set = PostSets::Pool.new(@pool, params[:page])
+    @posts = @pool.posts.paginate(params[:page], limit: params[:limit], count: @pool.post_count)
     respond_with(@pool)
   end
 

app/logical/post_query_builder.rb

@@ -433,6 +433,7 @@ class PostQueryBuilder
     if q[:ordpool].present?
       pool_id = q[:ordpool].to_i
 
+      # XXX unify with Pool#posts
       pool_posts = Pool.joins("CROSS JOIN unnest(pools.post_ids) WITH ORDINALITY AS row(post_id, pool_index)").where(id: pool_id).select(:post_id, :pool_index)
       relation = relation.joins("JOIN (#{pool_posts.to_sql}) pool_posts ON pool_posts.post_id = posts.id").order("pool_posts.pool_index ASC")
     end

app/models/pool.rb

@@ -213,21 +213,10 @@ class Pool < ApplicationRecord
     end
   end
 
-  def posts(options = {})
-    offset = options[:offset] || 0
-    limit = options[:limit] || Danbooru.config.posts_per_page
-    slice = post_ids.slice(offset, limit)
-    if slice && slice.any?
-      slice.map do |id|
-        begin
-          Post.find(id)
-        rescue ActiveRecord::RecordNotFound
-          # swallow
-        end
-      end.compact
-    else
-      []
-    end
+  # XXX unify with PostQueryBuilder ordpool search
+  def posts
+    pool_posts = Pool.where(id: id).joins("CROSS JOIN unnest(pools.post_ids) WITH ORDINALITY AS row(post_id, pool_index)").select(:post_id, :pool_index)
+    posts = Post.joins("JOIN (#{pool_posts.to_sql}) pool_posts ON pool_posts.post_id = posts.id").order("pool_posts.pool_index ASC")
   end
 
   def synchronize

app/views/pools/show.html.erb

@@ -15,9 +15,15 @@
     <%= render "posts/partials/common/inline_blacklist" %>
 
     <section>
-      <%= @post_set.presenter.post_previews_html(self) %>
+      <% if @pool.post_count == 0 %>
+        <%= render "post_sets/blank" %>
+      <% else %>
+        <% @posts.each do |post| %>
+          <%= PostPresenter.preview(post, pool_id: @pool.id) %>
+        <% end %>
 
-      <%= numbered_paginator(@post_set) %>
+        <%= numbered_paginator(@posts) %>
+      <% end %>
     </section>
   </div>
 </div>