Fields_for, how to use this data in controller - ruby-on-rails-4.2

Question

I'm lost onto how to use the data I get from using fields_for in rails. The array looks like this:
"order"=>{"order_item"=>{"1"=>{"quantity"=>"1"}, "2"=>{"quantity"=>"1"}}}
But I'm unsure on how to grab and use this data in a controller. For your information, I need to find the OrderItem by the id:
.. "order_item"=>{"1 (<-- this number is the id!)" .. and then update the quantity for that order_item.
I try to accept the params like this:
def order_params
params.require(:order).permit( order_item_attributes: [ :quantity ])
end
That should be correct, right?
in the controller I want to do something like this:
order_params[order_item_attributes].each do |item_id|
#orderitem = OderItem.find_by(id: item_id)
#orderitem.update(quantity: item_id[:quantity])
#... etc
I know the last code isn't correct, but I hope it helps you understand what I'm trying to do. I can find very little documentation on the fields_for and how to handle the data. Help would be welcome!
EDIT1:
This is what the view looks like
= form_for #order, :url => admin_update_order_path, :html => {:method => :post} do |f|
%table.detail_table
%tr
%th
%b Product
%th
%b Prijs
%th
%b Aantal
%th
%b Totaal
%th
%b Opties
- #order_items.each do |item|
%tr
%td
= item.product.name
%br
- x = 0
- item.product.product_attachments.each do |attachment|
-if item.product.id == attachment.product_id && x == 0
= image_tag attachment.image_url(:small)
- x = 1
%td= number_to_currency((item.product.price), :unit => "€", :separator => ",", :delimiter => ' ')
%td
= f.fields_for :order_items do |item_form|
= item_form.text_field :quantity, :class => "item_field"
%td= number_to_currency((item.product.price*item.quantity), :unit => "€", :separator => ",", :delimiter => ' ')
%td= link_to 'Verwijderen', item, method: :delete, data: { confirm: 'Weet u zeker dat u dit product uit dit order wilt verwijderen?' }
%br/
= f.submit
Thanks in advance

Answer 1

If you look at your params you are not passing in order_items_attributes you are passing order_item. Maybe if you change this you will have better luck.
The best way to test this is to fire up the rails console and copy your params into the console and see if you can get it working there. If you don't come right there then it wont work in the front end.
Also make sure that you have accepts_nested_attributes_for setup on your order model for order_items.
Edit 2
= f.fields_for item, index: item.id do |item_form|
= item_form.text_field
This above should be
= f.fields_for :order_items do |item_form|
= item_form.text_field
Your order model should have
has_many :order_items
accepts_nested_attributes_for :order_items
Your controller should permit params like so
def order_params
params.require(:order).permit( order_items_attributes: [:id :quantity])
end
Also if you want to get really funky with accepts_nested_attributes_for you should look into a gem called cocoon