Limiting Comments on Posts Index in Rails App

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

You should post the content of your partial too thats related to comments and say what kind of error are you getting with this. — Kleber S.

coreyward coreyward · Accepted Answer · 2011-04-12T03:16:48

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| %>

Limiting Comments on Posts Index in Rails App

1 Answers