AJAX update of accepts_nested_attributes_for partials

Question

My current working environment is Rails 2.3.8 (various reasons why my company hasn't moved to Rails 3). I'm trying to update elements of a multi-model form via AJAX calls - the idea being to replace certain dropdowns depending on how the user selects or fills in other fields.

I have previously managed to get this working by using non-form based partials - the problem I have now is to reproduce the AJAX updating of the select dropdowns when the partials are based around form_for and fields_for.

Sorry for the following wall of text - i've tried to cut it down as much as possible (the code itself does work on my test site).

How do I generate the form builder elements in the Outbreak controller and then pass this to the category partial to take the place of incident_form?

Any pointers would be great :D

Models

class Outbreak < ActiveRecord::Base
        has_many :incidents, :dependent => :destroy
        has_many :locations, :through => :incidents

     accepts_nested_attributes_for :locations, :allow_destroy => true, :reject_if => :all_blank
     accepts_nested_attributes_for :incidents, :allow_destroy => true, :reject_if => :all_blank
end

class Incident < ActiveRecord::Base
    belongs_to :outbreak
    belongs_to :location
    belongs_to :category
    belongs_to :subcategory
    belongs_to :subtype

end

class Location < ActiveRecord::Base
    has_many :incidents, :dependent => :destroy
     has_many :outbreaks, :thorugh => incidents
end

Views

_form

<% form_for(@outbreak, :html => {:multipart => true}) do |form| %>

  <%= render :partial => 'outbreak_type_select', :locals => {:outbreak_types => @outbreak_types, :f => form } %>
   <% form.fields_for :incidents do |incident_form| %>
      <%= render :partial => 'category_select', :locals => {:categories => @categories, :incident_form => incident_form} %>
      <%= render :partial => 'subcategory_select', :locals => { :subcategories => @subcategories, :incident_form => incident_form } %>

   <% end %>
<% end %>

_outbreak_type_select

<% with_str = "'outbreak_type=' + value " %>
<% if @outbreak.id %>
<% with_str << "+ '&id=' + #{outbreak.id}" %>
<% end %>
<%= f.collection_select(:outbreak_type, @outbreak_types, :property_value, :property_value, {}, {:onchange => "#{remote_function(:url  => { :action => "update_select_menus"}, :with => with_str)}"}  ) %>

_category_select

After calling update_select_menus how to generate the incident_form

<%= incident_form.collection_select( :category_id, @categories, :id, :name, {:prompt   => "Select a category"}, {:onchange => "#{remote_function(:url  => { :action => "update_subcategory"}, :with => "'category_id='+value")}"}) %>

RJS

   begin
    page.replace_html 'outbreak_transmission_div', :partial => 'outbreaks/transmission_mode_select', :locals => {:transmission_modes => @transmission_modes }
   rescue
    page.insert_html :bottom, 'ajax_error', '<p>Error :: transmission modes update select</p>'
    page.show 'ajax_error'
   end
   begin
    page.replace_html 'incident_category_select', :partial => 'outbreaks/category_select', :locals => { :categories => @categories }  
   rescue
    page.insert_html :bottom, 'ajax_error', '<p>Error :: incident category update select</p>'
    page.show 'ajax_error'
   end

Controllers

Outbreak

    def new
        @outbreak = Outbreak.new

        @outbreak.incidents.build
        @outbreak.locations.build

        #just the contents for the dropdowns
        @categories = Category.find(:all, :conditions => {:outbreak_type => "FOODBORNE"}, :order => "outbreak_type ASC")
        @subcategories = Subcategory.find(:all, :order => "category_id ASC")

    end

   def update_select_menus
      @outbreak_type = params[:outbreak_type].strip
      if params[:id]
        @outbreak = Outbreak.find(params[:id])
      else
        @outbreak = Outbreak.new
        @outbreak.incidents.build
              @outbreak.locations.build       
      end

      if @outbreak_type == "FOODBORNE"
          ob_type_query = "OUTBREAKS:TRANSMISSION_MODE:" << @outbreak_type
          @transmission_modes = Property.find(:all, :conditions => {:field => ob_type_query})

          ob_type_query = "INVESTIGATIONS:CATEGORY:" << @outbreak_type
          @sample_types = Property.find(:all, :conditions => {:field => ob_type_query})
          @categories = Category.find(:all, :conditions => { :outbreak_type => "FOODBORNE"})
          @subcategories = Subcategory.find(:all, :conditions => { :category_id => @categories.first.id})
          @subtypes = Subtype.find(:all, :conditions => { :subcategory_id => @subcategories.first.id})
      elsif @outbreak_type == "NON-FOODBORNE"
          ob_type_query = "OUTBREAKS:TRANSMISSION_MODE:" << @outbreak_type
          @transmission_modes = Property.find(:all, :conditions => {:field => ob_type_query})

          ob_type_query = "INVESTIGATIONS:CATEGORY:" << @outbreak_type
          @sample_types = Property.find(:all, :conditions => {:field => ob_type_query})
          @categories = Category.find(:all, :conditions => { :outbreak_type => "NON-FOODBORNE"})
          @subcategories = Subcategory.find(:all, :conditions => { :category_id => @categories.first.id})
          @subtypes = Subtype.find(:all, :conditions => { :subcategory_id => @subcategories.first.id})
     end

     respond_to do |format|
          format.html
          format.js
      end

  end

Answer 1

Found a work around based on http://www.treibstofff.de/2009/07/12/ruby-on-rails-23-nested-attributes-with-ajax-support/

This should probably go in Outbreak helper (in Outbreak controller atm)

    def update_select_menus
      @outbreak_type = params[:outbreak_type].strip
      #next_child_index will only be used if 
      @next_child_index ? params[:next_child_index] : 0
      if params[:id]
        @outbreak = Outbreak.find(params[:id])
      else
        @outbreak = Outbreak.new
        @outbreak.risks.build
        @outbreak.incidents.build
        @outbreak.locations.build

      end

      if @outbreak_type == "FOODBORNE"
          ob_type_query = "OUTBREAKS:TRANSMISSION_MODE:" << @outbreak_type
          @transmission_modes = Property.find(:all, :conditions => {:field => ob_type_query})

          ob_type_query = "INVESTIGATIONS:CATEGORY:" << @outbreak_type

          @sample_types = Property.find(:all, :conditions => {:field => ob_type_query})
          @categories = Category.find(:all, :conditions => { :outbreak_type => "FOODBORNE"})
          @subcategories = Subcategory.find(:all, :conditions => { :category_id => @categories.first.id})
          @subtypes = Subtype.find(:all, :conditions => { :subcategory_id => @subcategories.first.id})


      elsif @outbreak_type == "NON-FOODBORNE"
          ob_type_query = "OUTBREAKS:TRANSMISSION_MODE:" << @outbreak_type
          @transmission_modes = Property.find(:all, :conditions => {:field => ob_type_query})

          ob_type_query = "INVESTIGATIONS:CATEGORY:" << @outbreak_type

          @sample_types = Property.find(:all, :conditions => {:field => ob_type_query})
          @categories = Category.find(:all, :conditions => { :outbreak_type => "NON-FOODBORNE"})
          @subcategories = Subcategory.find(:all, :conditions => { :category_id => @categories.first.id})
          @subtypes = Subtype.find(:all, :conditions => { :subcategory_id => @subcategories.first.id})
     end

     @pathogen_types = Property.find(:all, :conditions => {:field => "PATHOGENS:CATEGORY"})
     @outbreak_types = Property.find(:all, :conditions => {:field => "OUTBREAKS:OUTBREAK_TYPE"} )


     render :update do |page|
         page.replace 'outbreak_transmission_div', :partial => 'transmission_mode_select_update'
         page.replace 'incident_category_select', :partial => 'incident_category_select_update'
         page.replace 'incident_subcategory_select', :partial => 'incident_subcategory_select_update'
         page.replace 'incident_subtype_select', :partial => 'incident_subtype_select_update'
     end      

  end

In the Outbreak view (although since this partial is related to Incident it should probably go in that view instead)

    <% ActionView::Helpers::FormBuilder.new(:outbreak, @outbreak, @template, {}, proc{}).fields_for :incidents,{:child_index => @next_child_index} do |this_form| %>
<div id="incident_category_select">
<%= render :partial => 'category_select', :locals => {:incident_form => this_form } %>
</div>
<% end %>

The ActionView::Helpers::FormBuilder is used to produce the required fields_for form - The website article goes through this in more detail.

The resulting index is set by the @next_child_index variable which can be passed to the controller by the original AJAX call (for example @next_child_index = 1, then the resulting form element name will be outbreak [incidents_attributes] [1] [category_id] ) - I haven't used this in this example because although in future I want the form to support more than one location per Outbreak for this initial run-through it will just accept a single Location - Incident per Outbreak.

_category_select.erb partial (in Outbreak view atm)

<% with_str = "'category_id=' + value " %>
<% if @outbreak.id %>
<% with_str << "+ '&id=' + #{@outbreak.id}" %>
<% end %>
<%= incident_form.collection_select( :category_id, @categories, :id, :name, {:prompt   => "Select a category"}, {:onchange => "#{remote_function(:url  => { :action => "update_subcategory"}, :with => with_str)}"}) %>

The with_str is just to optionally pass the Outbreak id if it exists to the controller to find the Outbreak record to produce the form and if not to build a new Outbreak and associated nested attributes like Incidents and Locations.

The must be neater ways of doing this - especially the FormHelper and passing the Outbreak id via the optional with string.