Question

I have worked with rails scaffold to generate forms and views automatically.
But now I had to use namespaced controller with model in root namspace.

So, I generated controller manually without scaffold, I’m having trouble working with form.

I suppose that the following code should generate a form for namespaced controller

<%= form_for @menu do |f| %>

  <div class="field">
    <%= f.label :label %><br />
    <%= f.text_field :label %>
  </div>
  <div class="field">
    <%= f.label :order %><br />
    <%= f.text_field :order %>
  </div>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

but it doesnt. it says

undefined method `model_name' for NilClass:Class

it seems very easy to do rails with scaffold generators, but if one wants to do manually, rails helper method turns negative on them.

I have searched for form_for documentation and changed the code to

<%= form_for @menu, :url => admin_menu_path do |f| %>

then it shows a different error that

No route matches {:action=>"show", :controller=>"admin/menus"}

my rake routes gives the following output

     admin_root        /admin(.:format)                admin/menus#index
    admin_menus GET    /admin/menus(.:format)          admin/menus#index
                POST   /admin/menus(.:format)          admin/menus#create
 new_admin_menu GET    /admin/menus/new(.:format)      admin/menus#new
edit_admin_menu GET    /admin/menus/:id/edit(.:format) admin/menus#edit
     admin_menu GET    /admin/menus/:id(.:format)      admin/menus#show
                PUT    /admin/menus/:id(.:format)      admin/menus#update
                DELETE /admin/menus/:id(.:format)      admin/menus#destroy

correct me if I’m wrong, but I think ruby cannot find model Menu in Admin namespace, which is obvious. So, I tried with ::Menu.new , I thought it would look up in upper namespace, but no result!

Answer 1

You might be forgetting to instantiate @menu in your controller.

The message “undefined method ‘model_name’ for NilClass:Class” says that @menu is nil.

Since admin_menu_path needs a Menu instance, Rails cannot generate the route correctly when nil is passed.

Once you have the instance variable properly set in your controller you can use:

form_for [:admin, @menu] do |f| ... end