Question

I am learning ruby on rails with the Getting Started tutorial on the official site here. http://guides.rubyonrails.org/getting_started.html

The only thing I have changed is the post url mapping to point to /post/friendly-url instead of /post/id

Everything has gone smooth until I try to add a comment to a post, I receive the following error.

NoMethodError in CommentsController#create

undefined method `comments' for nil:NilClass
app/controllers/comments_controller.rb:7:in `create'

Here is my code.

/app/controllers/comments_controller.rb

class CommentsController < ApplicationController
    def create
        @post = Post.find_by_friendly(params[:id])
        @comment = @post.comments.create(params[:comment])
        redirect_to post_path(@post)
    end

    def destroy
        @post = Post.find_by_friendly(params[:id])
        @comment = @post.comments.find(params[:id])
        @comment.destroy
        redirect_to post_path(@post)
    end
end

/app/models/comment.rb

class Comment < ActiveRecord::Base
    belongs_to :post

    attr_accessible :body, :commenter

    validates :body,  :presence => true
    validates :commenter,  :presence => true
end

/app/views/comments/_form.html.erb

<%= form_for([@post, @post.comments.build]) do |f| %>

<%= f.label :commenter, "Your Name:" %>
    <%= f.text_field :commenter, :placeholder => "Your Name..." %>
<span class="help-block">What would you like to be called.</span><br/>

<%= f.label :body, "Your Comment:" %>
    <%= f.text_area :body, :size => "60x12", :placeholder => "Your Comment..." %>
<span class="help-block">What's on your mind?</span><br/>

    <%= f.submit %>

<% end %>

/app/views/posts/_form.html.erb

<% @post.tags.build %>
<%= form_for(@post) do |post_form| %>
<legend>Post Form</legend>
<% if @post.errors.any? %>
    <div id="error_explanation">
        <h2 class="text-error"><%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:</h2>
        <ul>
            <% @post.errors.full_messages.each do |msg| %>
                <li class="text-error"><%= msg %></li>
            <% end %>
        </ul>
    </div>
<% end %>

<%= post_form.label :name, "Post Name:" %>
    <%= post_form.text_field :name, :placeholder => "Post Name..." %>
<span class="help-block">The title of the article.</span><br/>

<%= post_form.label :friendly, "Friendly URL:" %>
    <%= post_form.text_field :friendly, :placeholder => "Friendly URL..." %>
<span class="help-block">SEO friendly URL displayed as /posts/post-name.</span><br/>

<%= post_form.label :content, "Post Content:" %>
<%= post_form.text_area :content, :size => "60x12", :placeholder => "Main Content..." %>
<span class="help-block">HTML enabled article content.</span><br/>

<%= post_form.label :excerpt, "Post Excerpt:" %>
    <%= post_form.text_area :excerpt, :placeholder => "Post Excerpt..." %>
<span class="help-block">Description of post for index page. No HTML.</span><br/>

<h2>Tags</h2>
<%= render :partial => 'tags/form',
    :locals => {:form => post_form} %><br/>

    <%= post_form.submit %>

<% end %>

/config/routes.rb

Nullpulse::Application.routes.draw do
    resources :posts do
        resources :comments
    end

    root :to => "home#index"
end

/apps/models/post.rb

class Post < ActiveRecord::Base
    attr_accessible :content, :friendly, :name, :excerpt, :tags_attributes

    validates :name,  :presence => true
    validates :content, :presence => true
    validates :friendly, :presence => true
    validates :excerpt, :presence => true
    validates_format_of :friendly, :with => /^[^ ]+$/

    has_many :comments, :dependent => :destroy
    has_many :tags

    accepts_nested_attributes_for :tags, :allow_destroy => :true,
        :reject_if => proc { |attrs| attrs.all? { |k, v| v.blank? } }

    def to_param
        friendly
    end
end

Sorry if that is too much information, also please let me know if I am missing anything. I have been trying everything and I can’t find the issue. Thanks in advance.

Answer 1

The issue is that your @post in CommentController#create is nil. Which means, either your params[:id] that you’re providing is incorrect, or it isn’t being found in your database. I’d suggest checking the logs to see what params[:id] contains, and see if that matches what find_by_friendly is expecting.

If the params[:id] looks correct, I’d use the rails console to try the Posts.find_by_friendly and pass in some values to see if that works for you.

If the params[:id] value doesn’t look correct, then your form_for() call in comments/_form.html.erb is probably wrong, take a look at the docs for the friendly plugin to see how to make the correct call.