How to access nested objects in strong params - ruby-on-rails

Question

Hello I'm quite new to rails API. I'm having trouble on how can I access the :guest object from the params. What I want to to do is to create a new record in Booking and Guest. Thank you.
Booking Controller
attr_accessor :guest
def create
booking = Booking.new(reservation_params)
booking.guest.build({booking_id: booking.id, first_name: ?, last_name: ?})
end
def reservation_params
params.require(:booking).permit(:start_date, :end_date :guest => [:first_name, :last_name])
end
POST
{
"start_date": "2021-03-12",
"end_date": "2021-03-16",
"guest": {
"first_name": "John",
"last_name": "Doe",
}
}

Answer 1

1. You're assigning a local variable - not an instance variable.
attr_accessor :guest
def create
booking = Booking.new(reservation_params)
end
Here you might assume that since you declared a setter with attr_accessor that this would set the instance variable #booking so that you can access it from the view? Wrong. When performing assignment you need to explicitly set the recipient unless you want to assign a local variable.
attr_accessor :guest
def create
self.booking = Booking.new(reservation_params)
end
But you could actually just write #booking = Booking.new(reservation_params) since that setter is not actually doing anything of note.
2. Models don't have an id until they are saved.
This line:
booking.guest.build({booking_id: booking.id, first_name: ?, last_name: ?})
Is actually equivilent to:
booking.guest.build(booking_id: nil, first_name: ?, last_name: ?)
One big point of assocations is that the ORM takes care of linking the records for you. Let it do its job. If you're ever assigning an id manually in Rails you're most likely doing it wrong.
3. You're not saving anything to the DB
.new (build is just an alias for new) just instanciates an new model instance. You need to actually save the object for it to have any effect beyond the current request.
How do I fix it?
If you want to use that parameter structure it can be done with a bit of slicing and dicing:
def create
#booking = Booking.new(reservation_params.except(:guest)) do |b|
b.guest.new(reservation_params[:guest])
end
if #booking.save
redirect_to #booking
else
render :new
end
end
The reason you use except(:guest) to remove the guest param is that the setter defined by the assocation expects an instance of guest and not a hash so it will blow up otherwise
Nested attributes
accepts_nested_attributes is the Rails way of passing attibutes through another model. It expects the parameter to be named guest_attributes not guest.
class Booking < ApplicationRecord
belongs_to :guest
accepts_nested_attributes_for :guest
end
If you really need to use the existing params structure you can just alter the parameters in your whitelisting method:
class BookingsController < ApplicationController
# ...
def create
#booking = Booking.new(reservation_params)
if #booking.save
redirect_to #booking
else
render :new
end
end
private
def reservation_params
params.require(:booking)
.permit(:start_date, :end_date, guest: [:first_name, :last_name])
.tap do |p|
# replaces the key :guests with :guest_attributes
p.merge!(guest_attributes: p.delete(:guest))
end
end
end

Answer 2

You're trying to create two associated models as once, you can use:
accepts_nested_attributes_for.
In the booking model add:
# models/booking.rb
accepts_nested_attributes_for :guest
And then in the controller:
def reservation_params
params.require(:boking).permit(:start_date,...,
guest_attributes: [:first_name, :last_name])
end
And then you can just create the booking including the guest like so:
booking = Booking.new(reservation_params)
Find more info here:
https://api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html