undefined method `has_many' for Formtastic

Question

I'm getting this error :

undefined method `has_many' for #<Formtastic::SemanticFormBuilder:0xb410d4c>

It work when I use it like this :

ActiveAdmin.register Ressource do
    form do |f|  
        f.inputs do
            f.input :offer_id, :as => :hidden
            f.input :name
            f.input :category, :include_blank => false, :collection => Category.order('place ASC').all, :member_label => :to_label
            f.input :description, :input_html => {:class => 'editor'}
            f.input :price
        end
        f.has_many :roles do |app_f|
            app_f.inputs do
                if not app_f.object.id.nil?
                    app_f.input :_destroy, :as => :boolean, :label => "Supprimer l'utilisateur du lot"
                end
                app_f.input :user, :member_label => :to_label, :label => 'Assigné le lot'
                app_f.input :name, :include_blank => false
            end
        end
        f.buttons
    end
end 

But it doesn't work in a partial, i need to call the has_many method by a different way or something else ?

Answer 1

ActiveAdmin extends formtastic with some useful helpers such as has_many (lib/active_admin/form_builder.rb in the activeadmin gem).

Unfortunately, these helpers are not available by default in your templates.

Here are two options:

1. If you don't need the extra has_many functionality (it looks like active_admin adds some javascript to make it easy to add a new record to the collection), then you can use stock formtastic. This example should work fine in the activeadmin file as well as in a partial:

   ActiveAdmin.register Ressource do
     form do |f|  
       # ...
       f.inputs :for => :roles do |app_f|
         # ...
         app_f.input :name, :include_blank => false
       end
       f.buttons
     end
   end 
   

2. Use the ActiveAdmin form builder explicitly:

   <%= semantic_form_for [:admin, @resource], builder: ActiveAdmin::FormBuilder do |f| %>
     <!-- ... -->
   
     <%= f.has_many :teachers do |app_f| %>
       <%= app_f.inputs do %>
         <!-- ... -->
       <% end %>
     <% end %>
   
     <%= f.buttons %>
   <% end %>
   

I hope this helps.