irb.rb

Encoding.default_internal
# => #<Encoding:UTF-8>

Encoding.default_external
# => #<Encoding:UTF-8>

Order.select.keys.first.encoding
# => #<Encoding:ASCII-8BIT>

Order.select.values.first.encoding
# => #<Encoding:ASCII-8BIT>

order.rb

# coding: utf-8

require_relative "order_item"
require_relative "customer"
require_relative "payment_type"

class Order
  include DataMapper::Resource
  PER_PAGE ||= 20
  validates_present :customer, message: "Zákazník musí být vyplněn"
  belongs_to :customer
  belongs_to :payment_type
  has n, :items, class_name: "OrderItem"

  property :variable_symbol, Integer, key: true, auto_validation: false#, writer: :private
  property :status, Enum[:unprocessed, :processed], default: :unprocessed
  property :created_at, DateTime
  property :updated_at, DateTime
  property :referer, String
  property :note, Text
  
  # here we select data from db
  # the data must be in UTF-8, but they are in US-ASCII (see irb.rb)
  def self.select
    instances = Hash.new
    PaymentType.all.each do |instance|
      instances[instance.shortcut] = instance.name
    end
    return instances
  end
end