Defining users within partials - ruby-on-rails

Question

I am new to ruby on rails, and know this is a beginner error. I'm trying to create an application that displays user comments within a post. I have a comment partial pointing to my post#show, and when requesting to display <%= image_tag(comment.user.avatar.small.url, class: "media-object") if comment.user.avatar? %> from _comment.html.erb, I get "undefined method 'user' for nil:NilClass. I've read other questions on stackoverflow and I know this is saying it can't find a user associated with the post within comments and that I need to define user in my controller. I'm assuming it's for the post controller, but I can't seem to wrap my head around the specific syntax to display comments by user in post.
#comments_controller
def create
#topic = Topic.find(params[:topic_id])
#post = Post.find(params[:post_id])
#comment = current_user.comments.new(comment_params)
#comment.post = #post
#comment.save
authorize #comment
redirect_to [#topic, #post]
end
#posts_controller
def show
#topic = Topic.find(params[:topic_id])
#post = Post.find(params[:id])
end
#post model
class Post < ActiveRecord::Base
belongs_to :user
belongs_to :topic
has_one :summary
has_many :comments
mount_uploader :image, ImageUploader
#comment model
class Comment < ActiveRecord::Base
belongs_to :post
belongs_to :user
#rendering comment partial in post#show
<h1><%= #post.markdown_title %></h1>
<div class="row">
<div class="col-md-8">
<small>
<%= image_tag(#post.image.thumb.url) if #post.image? %></br>
<%= image_tag(#post.user.avatar.tiny.url) if #post.user.avatar? %>
submitted <%= time_ago_in_words(#post.created_at) %> ago by
<%= #post.user.name %>
</small>
<p><%= #post.markdown_body %></p>
</div>
<div class="col-md-4">
<% if policy(#post).edit? %>
<%= link_to "Edit", edit_topic_post_path(#topic, #post), class: 'btn btn-success' %>
<% end %>
<% if policy(#post).destroy? %>
<%= link_to "Delete Post", [#topic, #post], method: :delete, class: 'btn btn-danger', data: { confirm: "Are you sure you want to delete this post?" } %>
<% end %>
</div>
<div class="col-md-8">
<% if policy(Comment.new).create? %>
<%= render partial: 'comments/comment', locals: { comment: #comment } %>
<%= render partial: 'comments/form', locals: {topic: #topic, post: #post} %>
<% else %>
<h3>Sign up to Bloccit to post comments</h3>
<%= link_to "Sign up", new_user_registration_path, class: 'btn btn-primary' %></br></br>
<% end %>
#comment partial
<ul>
<% #post.comments.each do |c| %>
<div class="media">
<div class="media-left">
<%= image_tag(comment.user.avatar.small.url, class: "media-object") if comment.user.avatar? %>
</div>
<div class="media-body">
<small>
<%= comment.user.name %> commented <%= time_ago_in_words(comment.created_at) %> ago
<% if policy(comment).destroy? %>
| <%= link_to "Delete", [#topic, #post, comment], method: :delete %>
<% end %>
</small>
<li>
<p><%= c.body %></p>
</li>
</div>
<% end %>
Also, when I put #post.user = #user in posts_controller the error changes to "undefined method 'avatar' for nil:NilClass. Thanks for your help!

Answer 1

undefined method 'user' for nil:NilClass
The error is because of this line
<%= render partial: 'comments/comment', locals: { comment: #comment } %>
You don't have #comment initialized in show method of posts_controller and you are passing it as locals for comment, so comment.user returns error.
And also I've noticed that in _comment.html.erb you have this line <% #post.comments.each do |c| %>, so you can use c instead of comment.
<%= image_tag(c.user.avatar.small.url, class: "media-object") if c.user.avatar? %>

Answer 2

You are incorrectly referencing the block variable. Either change |c| to |comment| or change the comment references to c.
So like this:
<%= image_tag(c.user.avatar.small.url, class: "media-object") if c.user.avatar? %>