Rails / Formtastic-未进行验证

<%= semantic_form_for @user do |f| %>
  <ul class=\"formItem\">         
    <%= f.input :username, :required => true, :label => \"Your Username\", :input_html => { :class => \'double\' } %><br clear=\"all\" />
    <p class=\"fieldExplanation\">Your username is made public to other people on the site.</p>                       
  </ul> 
  <ul class=\"actions\">      
    <%= f.commit_button(\"Save my profile and make a match >\", :class => \"submitForm\") %>    
  </ul>
<% end %>

def update
 @user = User.find(params[:id])     
 respond_to do |format|
   if @user.update_attributes(params[:user])        
      format.html { redirect_to(match_user_path(@user), :notice => \'User was successfully updated.\') }              
   else
     format.html { render :action => \"edit\" }        
   end
 end
end