Rails updating multiple models on a single form

Im writing a form which uses formtastic to manage the BusinessUnit model, however when creating a new BusinessUnit it also has to create a number of other record types. The associations between the models are as below:

class BusinessUnit < ActiveRecord::Base
  has_many :business_unit_sites
  has_many :locations

class BusinessUnitSite < ActiveRecord::Base
  bel开发者_C百科ongs_to :site
  belongs_to :business_unit

class Site < ActiveRecord::Base
  has_many :locations
  has_many :business_unit_sites

class Location < ActiveRecord::Base
  belongs_to :business_unit
  belongs_to :site 

When a BusinessUnit is created, a Site must also be created using BusinessUnitSite as a join table. In addition a Location record should be created which must hold a foreign key to the new Site record and this is where Im having problems.

I can create a new Location using a nested form (below) but the Site will have to be created manually.

<%= semantic_form_for @business_unit do |f| %>
  <%= f.inputs do %>
    <%= f.input :name %>
    <%= f.input :business_unit_id %>
    <%= f.input :business_unit_group, :include_blank => false %>
    <%= f.input :business_unit_type %>
    <%= f.input :tax_region, :include_blank => false %>
    <%= f.semantic_fields_for :locations do |l| %>
      <%= l.input :name, :label => "Location Name" %>
    <% end %>
  <% end %>
  <%= f.buttons %>
<% end %>

What is the best way to create the Location, Site records and ensure that Location holds the foreign key of the newly created Site?

You probably want to do something like using the "fields_for" approach for the sub-objects in your form.

See this related answer: Multiple objects in a Rails form

More info about fields_for:

http://api.rubyonrails.org/classes/ActionView/Helpers/FormHelper.html

http://apidock.com/rails/ActionView/Helpers/FormHelper/fields_for