gistfile1.rb

# db/schema.rb
create_table "feed_items", :force => true do |t|
  t.integer  "user_id"
  t.integer  "post_id"
  t.datetime "post_created_at"
end

add_index "feed_items", ["user_id", "post_created_at"], :name => "index_feed_items_on_user_id_and_post_created_at"

gistfile2.rb

# app/models/user.rb
class User < ActiveRecord::Base
  has_many :feed_items
  has_many :posts
end

# app/models/post.rb
class Post < ActiveRecord::Base
  belongs_to :user
end

# app/controllers/feed_items_controller.rb
class FeedItemsController < ApplicationController
  def index
    @feed_items = current_user.feed_items.all(:limit => 30, :order => 'feed_items.post_created_at', :include => {:post => :user})
  end
end

# app/views/feed_items/index.html.erb
<% @feed_items.each do |feed_item| %>
  <p><%= feed_item.post.body %></p>
  <p>by <%= feed_item.user.name %></p>
<% end %>

gistfile3.txt

FeedItem Load (0.5ms)  SELECT "feed_items".* FROM "feed_items" LIMIT 30
Post Load (0.4ms)  SELECT "posts".* FROM "posts" WHERE ("posts"."id" IN (2,3))
User Load (0.5ms)  SELECT "users".* FROM "users" WHERE ("users"."id" IN (1,2))

gistfile4.rb

# Gemfile
gem 'json'

# db/schema.rb
create_table "feed_items", :force => true do |t|
  t.integer  "user_id"
  t.integer  "post_id"
  t.datetime "post_created_at"
  t.text     "post_cache" # adding this column
end

add_index "feed_items", ["user_id", "post_created_at"], :name => "index_feed_items_on_user_id_and_post_created_at"

# app/models/post.rb
class Post < ActiveRecord::Base
  def to_cache
    to_json :include => { :user => { :only => [:name] } }
  end
end

# app/models/feed_item.rb
class FeedItem < ActiveRecord::Base
  before_save :cache_post

  def cache_post
    self.post_cache = post.to_cache
  end

  def cached_post
    JSON.parse(post_cache)['post']
  end
end

# app/controllers/feed_items_controller.rb
class FeedItemsController < ApplicationController
  def index
    @feed_items = current_user.feed_items.all(:limit => 30, :order => 'feed_items.post_created_at')
  end
end

# app/views/feed_items/index.html.erb
<% @feed_items.each do |feed_item| %>
  <p><%= feed_item.cached_post['body'] %></p>
  <p>by <%= feed_item.cached_post['user']['name'] %></p>
<% end %>

gistfile5.txt

FeedItem Load (0.5ms)  SELECT "feed_items".* FROM "feed_items" LIMIT 30