Limiting Comments on Posts Index in Rails App - ruby-on-rails

Question

I am new to rails and trying to limit the number of comments displayed on my Posts Index Page to 2.
Below is my posts_controller:
class PostsController < ApplicationController
before_filter :authorize, :except => [:index, :show]
# GET /posts
# GET /posts.xml
def index
#posts = Post.all(:include => :comments, :order => "created_at DESC")
#comments = Comment.find(:all, :order => "created_at DESC", :limit => 1)
respond_to do |format|
format.html # index.html.erb
format.xml { render :xml => #posts }
end
end
# GET /posts/1
# GET /posts/1.xml
def show
#post = Post.find(params[:id])
respond_to do |format|
format.html # show.html.erb
format.xml { render :xml => #post }
end
end
# GET /posts/new
# GET /posts/new.xml
def new
#post = Post.new
respond_to do |format|
format.html # new.html.erb
format.xml { render :xml => #post }
end
end
# GET /posts/1/edit
def edit
#post = Post.find(params[:id])
end
# POST /posts
# POST /posts.xml
def create
#post = Post.new(params[:post])
respond_to do |format|
if #post.save
format.html { redirect_to(#post, :notice => 'Post was successfully created.') }
format.xml { render :xml => #post, :status => :created, :location => #post }
else
format.html { render :action => "new" }
format.xml { render :xml => #post.errors, :status => :unprocessable_entity }
end
end
end
# PUT /posts/1
# PUT /posts/1.xml
def update
#post = Post.find(params[:id])
respond_to do |format|
if #post.update_attributes(params[:post])
format.html { redirect_to(#post, :notice => 'Post was successfully updated.') }
format.xml { head :ok }
else
format.html { render :action => "edit" }
format.xml { render :xml => #post.errors, :status => :unprocessable_entity }
end
end
end
# DELETE /posts/1
# DELETE /posts/1.xml
def destroy
#post = Post.find(params[:id])
#post.destroy
respond_to do |format|
format.html { redirect_to(posts_url) }
format.xml { head :ok }
end
end
end
Below is my Post model
class Post < ActiveRecord::Base
has_attached_file :photo, :styles
=> { :medium => "600x600>", :thumb => "100x100>" },
:storage => :s3,
:s3_credentials => "#{RAILS_ROOT}/config/s3.yml",
:path => "/:attachment/:id/:style/:filename"
has_many :comments
validates :name, :presence => true
validates :title, :presence => true,
:length => { :minimum => 5 }
end
Below is my posts index view
<table>
<tr>
<th>BoxScore</th>
<th>Content</th>
</tr>
</table>
<% #posts.each do |post| %>
<%= image_tag post.photo.url(:medium), :class =>"floatleft" %>
<p>
<%= post.content %>
</p>
<div class="comments center">
<h3>Comments:</h3>
<%= render :partial => post.comments.reverse %>
<div class="links">
<% if admin? %>
<%= link_to "New Post", new_post_path %>
<%= link_to 'Edit', edit_post_path(post) %>
<%= link_to 'Destroy', post, :confirm => 'Are you sure?', :method => :delete %>
<% end %>
<%= link_to 'Comment on the Game', post %>
</div>
</div>
<% end %>
</div>
Comments Partial Below
<% div_for comment do %>
<p>
<strong>Posted <%= time_ago_in_words(comment.created_at) %> ago
</strong>
by
<br/>
<%= h(comment.commenter) %>
<br/>
<%= h(comment.body) %>
<br/>
<%= link_to 'More Comments', comment.post %>
</p>
<% end %>
I am not getting an error message, I just don't know how to limit the amount of comments we are rendering on Posts index page. Thanks

Answer 1

You can't specify conditions on eager loaded associations, unfortunately. Likewise, you can't limit the number of rows returned based on a condition (to my knowledge, though there are a lot of things I don't know about SQL functions).
So you're stuck with either:
Load all of the comments for the posts you're displaying in a query, and limit the number shown in your application.
Load only 2 comments for each of the posts you're displaying individually.
The optimal solution depends on your use case. If you're expecting to show only 5 posts and have thousands of comments on each, option 1 might not be very performant and option 2 might be a good solution. If you are expecting to show more posts per page and have only a handful of comments on any one (the more likely scenario), the first option is going to be your best bet.
Option 1
# controller
#posts = Post.limit(20).all
#comments = Comment.find(#posts.collect &:id).group_by &:post_id
# view
<% #comments[#post.id].first(2).each do |comment| %>
...
<% end %>
Option 2
# controller
#posts = Post.limit(5).all
# view
<% post.comments.limit(2).each do |comment| %>