How can I add a related record from its parents partial?

I have a table of reviews and comments, where a review can have many comments.

How can I have the add new comment form held inside the review partial?

What I have at the moment gives a "undefined method `model_name' for NilClass:Class" error.

_review.html.erb

<div class="review">    
  <div class="review_content">
    <h2 class="review_partial_title"><%= review.title %></h2>        
    <p class="review_body"><%= review.body %></p>       
  </div>

  <div class="clearall"></div>

  <div class="comments_container">
    <%= render :partial => 'comments/comment',开发者_开发知识库 :collection => review.comments %>
  </div>

  <div class="add_comment_container">
    <%= form_for [@review, @comment] do |f| %>    
      <p>body: <br>
      <%= f.text_field :body %></p>

      <%= submit_tag %>
    <% end %>
  </div>
  <div class="clearall"></div>
</div>

review.rb

class Review < ActiveRecord::Base
  has_many :comments

  accepts_nested_attributes_for :comments
end

routes

resources :reviews do
  resources :comments
end

Thanks for any help its much appreciated!

Change this:

<%= form_for [@review, @comment] do |f| %>

To this:

<%= form_for [review, review.comments.build] do |f| %>

Hope that helps