Rails undefined method 'model_name' for nil:nilClass with nested attributes

Question

I have in my orders/edit.html.erb a form that begins like this:

<%= simple_form_for [@reservation, @order] do |f| %>

Orders Controller:

def edit
  @reservation = Reservation.find_by_id(params[:reservation_id])
  @order       = Order.find_by_id(params[:id])
end

Association:

Reservation :has_one Order

Routes:

resources :reservations do
  resources :orders 
end

If my path resembles something like /reservations/10/orders/10/edit I end up getting an error from Rails saying NoMethodError in Orders#edit and undefined method 'model_name' for nil:NilClass

When I create a new order the form works perfectly fine so not sure why i'm getting an error all of a sudden, can someone help me with this issue?

Change find_by_id to find ... could be wrong, but my guess is that the row does not exist; if so, find will blow up (properly, as you don't want to continue in this case anyway); find_by_id will just set things to nil, which will non-deterministically blow up somewhere along the way. — GoGoCarl
– GoGoCarl, Commented Apr 20, 2016 at 22:56
That definitely worked, please answer below so i can mark it as a solution! thanks so much! By the way, is there a way for find_by_id to 'blow up' so I can get the same error? @GoGoCarl — ayounis90
– ayounis90, Commented Apr 20, 2016 at 23:01
Thanks. See below for details on your second question. find_by_id won't ever blow up, it'll always return nil if the record isn't found. But you can handle that case manually. — GoGoCarl
– GoGoCarl, Commented Apr 20, 2016 at 23:11

GoGoCarl · Accepted Answer · 2016-04-20 23:10:06Z

2

Current implementation is prone to failure when the URL supplied either a reservation ID or an order ID that is not valid. Two ways to handle this:

First, let Rails do it for you:

def edit
  @reservation = Reservation.find(params[:reservation_id])
  @order       = Order.find(params[:id])
end

This will raise an ActiveRecord::RecordNotFound error, which, in production, should lead users to your 404 page.

If you'd prefer to keep find_by_id and handle this manually, or to rescue from this error in a different way, you can do:

def edit
  @reservation = Reservation.find_by_id(params[:reservation_id])
  @order       = Order.find_by_id(params[:id])

  if @reservation.nil? || @order.nil?
    raise ActiveRecord::RecordNotFound.new # Or, do something else
  end
end

That would yield the same result as above ... just more code.

answered Apr 20, 2016 at 23:10

GoGoCarl

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