title: Send url param from form_tag Rails
body: <p>this is my case:</p>
  
  <pre><code>I'm in /car
  </code></pre>
  
  <p>and I want to pass a car model through a form like:</p>
  
  <pre><code>/car/:model for example /car/bmw+z4
  </code></pre>
  
  <p>This is my form:</p>
  
  <pre><code>&lt;%= form_tag(get_model_path, :method =&gt; 'get') do |f| %&gt;
    &lt;%= f.text_field, :model %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>And an error message says:</p>
  
  <pre><code>No route matches {:action=&gt;"get_model", :controller=&gt;"cars"} missing required keys: [:model]
  </code></pre>
  
  <p>All this without model or activerecord, becouse is an API consumption.</p>
  
  <p>Any idea?</p>