How to duplicate a record and its associated records in Ruby on Rails?

Question

In my Rails app I have invoices and their associated items.

In my InvoicesController I added this method:

def duplicate
  invoice = Invoice.find(params[:id])
  @invoice = invoice.dup
  invoice.items.each do |item|
    @invoice.items << item
  end      
  render :new    
end

def create
  @invoice = current_user.invoices.build(params[:invoice])    
  if @invoice.save
    flash[:success] = "Invoice created."
    redirect_to edit_invoice_path(@invoice)
  else
    render :new
  end
end

Clicking the link instantiates a form with the correct invoice and items data.

However, when trying to Create the record I get an error:

Couldn't find Item with ID=4 for Invoice with ID=

Can anybody tell me what I am missing here or if there's a smarter way to duplicate a record including its associated records?

Thanks for any help.

Answer 1

Here's cose that will duplicate the main object, and each of the items underneath it. The new object will not be saved, nor will the items (yet).

  def duplicate
    dup.tap do |new_invoice|
      items.each do |item|
        new_invoice.items.push item.dup
      end
    end
  end

And a quick test to prove the things:

require 'test_helper'

class InvoiceTest < ActiveSupport::TestCase

  def original_invoice
    Invoice.create(number: 5).tap do |invoice|
      invoice.items.create(name: "a", price: "5")
      invoice.items.create(name: "b", price: "50")
    end
  end
  test "duplication" do
    new_invoice = original_invoice.duplicate
    new_invoice.save
    assert_equal 2, new_invoice.items.count
  end
end