title: rails 4 simple_form as: hidden don't send
body: <p>I have this code:</p>
  
  <pre><code>&lt;%= simple_form_for(@uniform) do |f| %&gt;
      &lt;%= f.error_notification %&gt;
      &lt;%= f.association :employee, as: :hidden, selected: @employee %&gt;
      &lt;%= f.association :piece %&gt;
      &lt;%= f.button :submit, "Add new piece" %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>But, the hidden field ":employee", don't send the selected employee, only send if this "f.association" is not hidden.</p>
  
  <p>My controller is default scaffold:</p>
  
  <pre><code>def create
      @uniform = Uniform.new(uniform_params)
  
      respond_to do |format|
          if @uniform.save
              format.html { redirect_to @uniform, notice: 'Uniform was successfully created.' }
          else
              format.html { render action: 'new' }
          end
      end
  end
  </code></pre>
  
  <p>I need to send this value of "f.association :employee" but without show in the browser.</p>