title: ActionController::UrlGenerationError missing required keys: [:id]
body: <p>I am very new at ruby - trying out rails and I am stuck already trying to do a simple register form:</p>
  
  <pre><code>&lt;%= form_for :user, url: user_path do |f| %&gt;
      &lt;p&gt;
        &lt;%= f.label :email %&gt;&lt;br&gt;
        &lt;%= f.text_field :email %&gt;
      &lt;/p&gt;
  
      &lt;p&gt;
        &lt;%= f.label :password %&gt;&lt;br&gt;
        &lt;%= f.password_field :password %&gt;
      &lt;/p&gt;
  
      &lt;p&gt;
        &lt;%= f.submit %&gt;
      &lt;/p&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>This is giving an error:</p>
  
  <pre><code>No route matches {:action=&gt;"show", :controller=&gt;"user"} missing required keys: [:id]
  </code></pre>
  
  <p>Can anyone explain what this actually means?</p>
  
  <p>EDIT:</p>
  
  <p>I am following this tutorial, only changing posts to user: <a href="http://guides.rubyonrails.org/getting_started.html">http://guides.rubyonrails.org/getting_started.html</a></p>