ajax check username available in rails

1, Client

<%=link_to_remote 'Check Availability',

   :submit   => "signupForm",

   :url => {:controller => 'users', :action => 'check_username_avaiable' },

   :update => 'check_username',

   :html => {:class => 'smallText'} %>

 注意这里的submit 是Form的ID, update是ajax回来以后要update的DOM的ID 

2, server

  def check_username_avaiable

    exist_user = User.find_by_username(params[:username])

    exist_user = 'yes' if params[:username] == 'demo'

    if exist_user.nil? then

      render :partial=>'username_avaiable', :locals => {:username => params[:username]}

    else

      render :partial=>'username_not_avaiable', :locals => {:username => params[:username]}

    end

  end