Question

Im new to ruby and rails, however I cant figure out why this doesnt work.

I am doing a simple Blog with posts and its comments, everything works fine but I tried to do my own method inside Post model to get the latest comment inside that post.

class Post < ActiveRecord::Base
  attr_accessible :content, :title

  has_many :comments

    def latestComment(id)
        post = Post.find(id)
        comment = post.comments.last
    end
  end

and the index.html.erb

<h1>Hello World!</h1>

<h2>Posts</h2>

<% @posts.each do |post| %>

    <h3><%= link_to post.title, post %></h3>
    <p><%= post.content %></p>

    <%= latestComment = post.latestComment(post) %>

<% end %>

<h3>Add new post</h3>
<%= link_to "Add new post", new_post_path %>

This works, it returns some hexa values, so the object exists, however then I now want to get fields from that object like this

<p><%= latestComment.author %></p>
<p><%= latestComment.content %></p>

It fails and the error is

undefined method `author' for nil:NilClass

which is weird and I dont get it why cant I access comments fields..

///comment.rb

class Comment < ActiveRecord::Base
    attr_accessible :author, :content, :post_id

    belongs_to :post
end

Answer 1

Since you are looping over multiple posts, it’s possible that one of them doesn’t have any comments, which makes post.comments.last return nil. You can work around this by checking it before trying to render the comment:

class Post < ActiveRecord::Base
  def has_comments?
    comments.count > 0
  end

  def last_comment
    comments.last
  end
end

Then, on the view:

<% @posts.each do |post| %>

  <h3><%= link_to post.title, post %></h3>
  <p><%= post.content %></p>

  <% if post.has_comments? %>
    <p><%= post.last_comment.author %></p>
    <p><%= post.last_comment.content %></p>
  <% end %>
<% end %>