AddAuthorToComments Migration

class AddAuthorToComments < ActiveRecord::Migration
  def change
    add_reference :comments, :author, index: true
    add_foreign_key :comments, :users, column: :author_id
  end
end

Comment Class

class Comment < ActiveRecord::Base
  belongs_to :topic
  belongs_to :author, class_name: "User"
  validates :text, presence: true, length: { minimum: 15 }
end

CommentsController

class CommentsController < ApplicationController
  before_action :set_ticket
  before_action :set_comment, only: [:edit, :update]
  
  def edit
  end
  
  def update
  end
  
  def create
    @comment = @topic.comments.build(comment_params)
    
    @comment.author = current_user
    
    if @comment.save
      flash[:notice] = "Comment has been created."
      redirect_to [@topic.forum, @topic]
    else
      flash.now[:alert] = "Comment has not been created."
      render 'new'
    end
  end
  
  private
  
  def set_topic
    @topic = Topic.find(params[:topic_id])
  end
  
  def set_comment
    @comment = Comment.find(params[:id])
  end
  
  def comment_params
    params.require(:comment).permit(:text)
  end
end

hidden links methods

# Helper methods that hide certain links from users that aren't the author of a comment or post.

module ApplicationHelper
  def admins_only(&block)
    block.call if current_user.try(:admin?)
  end
  
  def topic_author_only(&block)
    block.call if current_user.email == @topic.author.email ||
    current_user.try(:admin?)
  end
  
  def comment_author_only(&block)
    block.call if current_user.email == @comment.author.email ||
    current_user.try(:admin?)
  end
end

Nil-Class error message

# The error message

Showing /home/ubuntu/workspace/app/views/topics/show.html.erb where line #35 raised:

undefined method `author' for nil:NilClass
Extracted source (around line #12):
10
11
12
13
14
15
              
  
  def comment_author_only(&block)
    block.call if current_user.email == @comment.author.email ||
    current_user.try(:admin?)
  end
end

Topic (#show) View

<div class='page-header'>
  <h1><%= @topic.title %></h1>
</div>

<table id='attributes'>
  <tr>
    <th>Author:</th>
    <td><%= @topic.author.email %></td>
  </tr>
  <tr>
    <th>Created: </th>
    <td> <%= time_ago_in_words(@topic.created_at) %> ago</td>
  </tr>
</table>

<h4><%= @topic.description %></h4>

<ul class='actions'>
  <li><%= link_to "Back", forum_path(@forum), class: 'btn btn-primary' %></li>
  <li><%= link_to "Add Comment", new_topic_comment_path(@topic, @comment), class: "new btn-primary" %></li>
   <% topic_author_only do %>
    <li><%= link_to 'Edit Topic', edit_forum_topic_path, class: "edit" %></li>
    <li><%= link_to "Delete Topic", [@forum, @topic], method: :delete,
    data: { confirm: "Are you sure you want to delete this topic?" }, class: "delete btn-danger" %></li>
  <% end %>
</ul>

<br>

<ul class="attributes">
  <% if @topic.comments.any? %>
    <% @topic.comments.each do |comment| %>
      <li><h4><%= comment.author.email %> -</li></h4>
      <li><%= comment.text %></li>
      <% comment_author_only do %>
        <li><%= link_to "Edit Comment", edit_topic_comment_path(@topic, @comment), class: "edit" %></li>
      <% end %>
    <% end %>
  <% else %>
    <p>There are no comments on this topic (yet!)</p>
  <% end %>
</ul>

<header>New Comment</header>

<%= render 'comments/form', ticket: @ticket, comment: @comment %>