Fix n+1 select query for book's index page

app/controllers/doc_controller.rb

@@ -1,7 +1,7 @@
 class DocController < ApplicationController
   layout "layout"
 
-  before_filter :book_resource, :only => [:index, :book, :book_section, :progit]
+  before_filter :book_resource, :only => [:index, :book_section, :progit]
 
   def index
     @videos = VIDEOS
@@ -66,6 +66,8 @@ def man
   end
 
   def book
+    @book = Book.includes(:sections).where(:code => (params[:lang] || "en")).first
+    raise PageNotFound unless @book
   end
 
   def book_section

app/models/chapter.rb

@@ -6,16 +6,17 @@ class Chapter < ActiveRecord::Base
   default_scope :order => 'number'
   belongs_to :book
   has_many :sections
+  has_many :chapters, :through => :book
 
   def prev
     num = self.number - 1
-    return self.book.chapters.where(:number => num).first if num > 0
+    return self.chapters.where(:number => num).first if num > 0
     false
   end
 
   def next
     num = self.number + 1
-    return self.book.chapters.where(:number => num).first if num > 0
+    return self.chapters.where(:number => num).first if num > 0
     false
   end
 

app/models/section.rb

@@ -13,6 +13,7 @@ class Section < ActiveRecord::Base
   has_one :book, :through => :chapter
   before_save :set_slug
   after_save :index
+  has_many :sections, :through => :chapter
 
   def get_related(limit = 10)
     ri = RelatedItem.where(:related_type => 'book', :related_id => slug).order('score DESC').limit(limit)
@@ -30,7 +31,7 @@ def set_slug
   def prev_slug
     lang = self.book.code
     prev_number = self.number - 1
-    if section = self.chapter.sections.where(:number => prev_number).first
+    if section = self.sections.where(:number => prev_number).first
       return "/book/#{lang}/#{section.slug}"
     else
       # find previous chapter
@@ -46,7 +47,7 @@ def prev_slug
   def next_slug
     lang = self.book.code
     next_number = self.number + 1
-    if section = self.chapter.sections.where(:number => next_number).first
+    if section = self.sections.where(:number => next_number).first
       return "/book/#{lang}/#{section.slug}"
     else
       if ch = self.chapter.next