Works fine on localhost, but not on heroku

Question

I have a problem on heroku, when I try to access my posts. The logs says:

Rendered posts/index.html.erb within layouts/application (920.6ms)
2015-11-06T09:39:41.716328+00:00 app[web.1]: Completed 500 Internal Server Error in 936ms (ActiveRecord: 42.1ms)
2015-11-06T09:39:41.720223+00:00 app[web.1]: 
2015-11-06T09:39:41.720226+00:00 app[web.1]: ActionView::Template::Error (undefined method `email' for nil:NilClass):
2015-11-06T09:39:41.720227+00:00 app[web.1]:     22:            <dt> <%= post.body %> </dt>
2015-11-06T09:39:41.720227+00:00 app[web.1]:     23:             <dd><%= post.tags %> </dd>
2015-11-06T09:39:41.720228+00:00 app[web.1]:     24:          </dl>
2015-11-06T09:39:41.720229+00:00 app[web.1]:     25:          <%= gravatar_for post.user, size: 40%> Created by <b><%= post.user.name if post.user %></b>
2015-11-06T09:39:41.720229+00:00 app[web.1]:     26:         </td>
2015-11-06T09:39:41.720230+00:00 app[web.1]:     27: 
2015-11-06T09:39:41.720231+00:00 app[web.1]:     28:     <div>
2015-11-06T09:39:41.720231+00:00 app[web.1]:   app/helpers/users_helper.rb:3:in `gravatar_for'

On localhos:3000/posts it works good, the mistake appears only on heroku. I use PostgreSQL both in development and production.

Here is my routes.rb:

  resources :users
  resources :sessions, only: [:new, :create, :destroy]
  resources :posts
 root 'posts#index'
   match '/signup', to: 'users#new',         via: 'get'
   match '/signin', to: 'sessions#new',      via: 'get'
   match '/signout', to: 'sessions#destroy', via: 'delete'

A part of my posts#index:

<div class="show_posts">
<table>
    <% @posts.each do |post| %>

        <td>
         <dl> <%= post.title %>
           <dt> <%= post.body %> </dt>
            <dd><%= post.tags %> </dd>
         </dl>
         <%= gravatar_for post.user, size: 40%> Created by <b><%= post.user.name if post.user %></b>
        </td>

users_helper.rb:

module UsersHelper
  def gravatar_for(user, options = { size: 50 })
    gravatar_id = Digest::MD5::hexdigest(user.email.downcase)
    size = options[:size]
    gravatar_url = "https://secure.gravatar.com/avatar/#{gravatar_id}?s=#{size}"
    image_tag(gravatar_url, alt: user.name, class: "gravatar")
  end
end    

Any ideas how to solve the problem?

Answer 1

The problem lies inside gravatar_for , where you call...

Digest::MD5::hexdigest(user.email.downcase)

The required user object doesn't exist.

This is caused in your posts#index model, when you reference:

<%= gravatar_for post.user, size: 40%> Created by <b><%= post.user.name if post.user %>

---

As suggested in the comments, this is likely due to you not having an associated user object for your post .

The immediate fix will be to use some conditional logic to determine whether the user exists (which you're doing already, but only for the post.user.name output):

<% if post.user %>
    <%= gravatar_for post.user, size: 40 %> Created by <b><%= post.user.name %>
<% end %>

Alternatively, you may wish to make all posts have a user by using a validation to determine whether the associated object is set:

#app/models/user.rb
class User < ActiveRecord::Base
   has_many :posts, inverse_of: :user
end

#app/models/post.rb
class Post < ActiveRecord::Base
   belongs_to :user, inverse_of: :posts
   validates :user, present: true
end