Atribut bersarang Rails yang beberapa di antaranya sudah ada menyebabkan permintaan basis data

Saya mencoba melakukan sesuatu yang menurut saya seharusnya sangat sederhana. Saya memiliki empat model sebagai berikut:

class Checkout < ActiveRecord::Base
  has_many :checkedout_items
  belongs_to :student, :autosave => true
  attr_accessible :student_id, :status, :checkedout_items_attributes, :student_attributes, :status
  accepts_nested_attributes_for :checkedout_items
  accepts_nested_attributes_for :student
end

class CheckedoutItem < ActiveRecord::Base
  belongs_to :checkout, :autosave => true
  has_one :item, :foreign_key => "id"
  attr_accessible :enddate, :checkout_id, :item_id, :startdate, :status, :item_attributes
  accepts_nested_attributes_for :item
end

class Item < ActiveRecord::Base
  attr_accessible :name, :category
end

class Student < ActiveRecord::Base
  has_many :checkouts, dependent: :destroy
  attr_accessible :email, :firstname, :lastname, :phonenumber, :uin
end

Saya ingin memiliki satu formulir di mana pengguna akhir dapat membuat siswa dan item_checkout dalam satu formulir. Jadi, saya memiliki tampilan yang membuat formulir dan menghasilkan struktur hash berikut:

{"utf8"=>"✓",
 "authenticity_token"=>"m6yH1LhtOk/kDqpLDRlNkxFSAA1WmGARywgT4DwYmKo=",
 "checkout"=> {
   "student_attributes"=> {
     "firstname"=>"Jimmy",
     "lastname"=>"Johnson",
     "uin"=>"899006555",
     "email"=>"[email protected]",
     "phonenumber"=>"1234445555"
   },
   "checkedout_items_attributes"=> {
     "0"=> {
       "item_attributes"=> {
         "id"=>"1",
         "name"=>"Camera #1"
       },
       "startdate(2i)"=>"12",
       "startdate(3i)"=>"8",
       "startdate(1i)"=>"2014",
       "startdate(4i)"=>"04",
       "startdate(5i)"=>"00"
     },
     "1"=> {
       "item_attributes"=> {
         "id"=>"2",
         "name"=>"Camera #2"
       },
       "startdate(2i)"=>"12",
       "startdate(3i)"=>"8",
       "startdate(1i)"=>"2014",
       "startdate(4i)"=>"04",
       "startdate(5i)"=>"00"
     }
   }
 },
"commit"=>"Finish"}

Ketika data ini diposting ke pengontrol saya, saya mencoba membuat objek checkout baru sebagai berikut:

@checkout = Checkout.new(params[:checkout])

Namun, hal ini menyebabkan kesalahan: "Tidak dapat menemukan Item dengan ID=1 untuk CheckedoutItem dengan ID=". Saya telah mencoba mencari masalah lain yang terkait dengan ini, tetapi saya tidak menemukan banyak.

Salah satu informasi penting terakhir adalah bahwa Item harus selalu ada sebelum checkout dibuat sehingga item dengan ID 1 dan 2 sudah ada di database. Adakah yang bisa memberikan wawasan tentang apa yang salah?

EDIT: Metode pengontrol:

def create
    @checkout = Checkout.new(params[:checkout])

    respond_to do |format|
      if @checkout.save
        format.html { redirect_to @checkout, notice: 'Checkout was successfully created.' }
        format.json { render json: @checkout, status: :created, location: @checkout }
      else
        format.html { render action: "new" }
        format.json { render json: @checkout.errors, status: :unprocessable_entity }
      end
    end
  end

Kesalahan:

Couldn't find Item with ID=2 for CheckedoutItem with ID=

Jejak sebagian:

activerecord (3.2.16) lib/active_record/nested_attributes.rb:487:in `raise_nested_attributes_record_not_found'
activerecord (3.2.16) lib/active_record/nested_attributes.rb:357:in `assign_nested_attributes_for_one_to_one_association'
activerecord (3.2.16) lib/active_record/nested_attributes.rb:313:in `item_attributes='
activerecord (3.2.16) lib/active_record/attribute_assignment.rb:94:in `block in assign_attributes'
activerecord (3.2.16) lib/active_record/attribute_assignment.rb:93:in `each'
activerecord (3.2.16) lib/active_record/attribute_assignment.rb:93:in `assign_attributes'
activerecord (3.2.16) lib/active_record/base.rb:498:in `initialize'
activerecord (3.2.16) lib/active_record/reflection.rb:183:in `new'
activerecord (3.2.16) lib/active_record/reflection.rb:183:in `build_association'
activerecord (3.2.16) lib/active_record/associations/association.rb:239:in `build_record'
activerecord (3.2.16) lib/active_record/associations/collection_association.rb:112:in `build'
activerecord (3.2.16) lib/active_record/nested_attributes.rb:430:in `block in assign_nested_attributes_for_collection_association'
activerecord (3.2.16) lib/active_record/nested_attributes.rb:425:in `each'
activerecord (3.2.16) lib/active_record/nested_attributes.rb:425:in `assign_nested_attributes_for_collection_association'
activerecord (3.2.16) lib/active_record/nested_attributes.rb:313:in `checkedout_items_attributes='
activerecord (3.2.16) lib/active_record/attribute_assignment.rb:94:in `block in assign_attributes'
activerecord (3.2.16) lib/active_record/attribute_assignment.rb:93:in `each'
activerecord (3.2.16) lib/active_record/attribute_assignment.rb:93:in `assign_attributes'
activerecord (3.2.16) lib/active_record/base.rb:498:in `initialize'

Versi rel: 3.2.16