Update multiple records in Rails 3

For some reason when I submit the form params[:user] array is not send (POST):

app/views/groups/edit.html.erb

http://localhost:3000/groups/2

<%= form_for @group do |f| %>
    <% @users.each_with_index do |u, n| %>
      <%= fields_for "users[#{n}]", u do |ff| %>
        <%= ff.select :city_id, grouped_options_for_select(City.states.map {|c| [c.state, City.by_state(c.state).map {|s| [s.name,s.id]}]}, u.city_id) %>
      <% end %>
    <% end %>
  <%= f.submit 'Update Users' %>
<% end %>

output

  <form accept-charset="UTF-8" action="/groups/2" class="edit_group" id="edit_group_2" method="post"><div style="margin:0;padding:0;display:inline"><input name="utf8" type="hidden" value="&#x2713;" /><input name="_method" type="hidden" value="put" /><input name="authenticity_token" type="hidden" value="iT3CGpXpQGxjjAGK9iv2I7x0cGr9d0pW6yc4svzTMFw=" /></div> 
    <select id="users_0_city_id" name="users[0][city_id]">
      <optgroup label="State1">
        <option value="1">City1</option> 
        <option value="2">City2</option> 
      </optgroup>
      <op开发者_Go百科tgroup label="State2">
        <option value="3">City3</option> 
        <option value="4">City4</option> 
      </optgroup>
    </select>
  </form>

sent parameters

http://localhost:3000/groups/2/edit

  Parameters: {"utf8"=>"✓", "authenticity_token"=>"iT3CGpXpQGxjjAGK9iv2I7x0cGr9d0pW6yc4svzTMFw=", "commit"=>"Update Users", "id"=>"2"}

Any help very appreciated

---

In your view:

<%= form_for @group do |f| %>
   <%= fields_for "users[#{n}]", u do |builder| %>
   <%= builder.select :city_id, grouped_options_for_select(City.states.map {|c| [c.state, City.by_state(c.state).map {|s| [s.name,s.id]}]}, u.city_id) %>
   <% end %>
   <%= f.submit 'Update Users' %>
<% end %>

In your Group model:

has_many :users
accepts_nested_attributes_for :users

In your controller make sure you build the users or they won't show up.

def new
   @group = Group.new
   users = User.all #obviously chose your own conditions
   @group.users = users
end