Move data from removed column to just created one in Rails migration

Question

I have a table 'Invoices' which contains two boolean columns:

Table name: invoices

id               :integer          not null, primary key
...
sent             :boolean          default(FALSE)
payment_received :boolean          default(FALSE)

This two columns define status of invoice:

def status
  if sent & payment_received
    :paid
  elsif sent | payment_received
    :sent
  else
    :created
  end
end

One day it was desided to remove these boolean columns and create new column that will contain invoice status by the help of Rails enum

status :integer

enum status: [ :created, :sent, :paid ]

So now I need to do 3 things:

1. Add new column 'status'
2. Calculate status for existing invoices, update status column
3. Remove columns 'sent' and 'payment_received'.

How can I do this? I can do this task easily on my local environment, but I can't understand how can I do this on production server. If, for example, I'll create a migration that update my table and a rake task that calculate status, migration pass first and my data from boolean columns will be removed before I can use them.

Note: if somehow it's important: I use Postgres.

Any help is appreciated!

Answer 1

Try the following migration.

class UpdateInvoicesTable < ActiveRecord::Migration
  def self.up
    add_column :invoices,:status,:string

    Invoice.find_in_batches(batch_size: 2000) do |invoices|
      invoices.each do |invoice|
        if invoice.sent & invoice.payment_received
          invoice.status = 'paid'
        elsif invoice.sent | invoice.payment_received
          invoice.status = 'sent'
        else
          invoice.status = 'created'
        end
        invoice.save
      end
    end

    remove_column :invoices,:sent
    remove_column :invoices,:payment_received
  end  
end