Rails 4 form_for associations - how to save/edit form?

Question

I have a mode Car that has many services.

class Car < ActiveRecord::Base
  has_many :car_services, dependent: :destroy
  has_many :services, through: :car_services
end

In the new controller action:

@car = Car.new
@car.car_services.build

And in the view _form.html.erb (the relevant part):

  <div class="edit_shipper_services">
    <%= f.association :services, 
                     as: :check_boxes, 
                     label_method: :label, 
                     value_method: :id,
                     label: 'Services' %>
  </div>

The checkboxes are nicely rendered, but when I try to create a new car, I get an error about

undefined method `name' for nil:NilClass

I have some imported data in the database and when I try to save an existing information, the same error will occur.

How I am creating a new car:

respond_to do |format|
  if @car.save
    ...

What am I missing?

Thank you.

Answer 1

it looks like your trying to save car and car_services in one form, in order too save the two in one form you need to use nested forms.

if you don't know how to use nested forms check out http://www.amooma.de/screencasts/2015-01-22-nested_forms-rails-4.2/ and http://railscasts.com/episodes/196-nested-model-form-part-1