Custom attribute types for accessors in Rails 6

# config/initializers/attribute_types.rb
ActiveRecord::Type.register(:discount_line_type, DiscountLineType)

# discount_line_type.rb
class DiscountLineType < ActiveRecord::Type::Value
  DISCOUNT_LINE = Struct.new(:name, :description, :amount, keyword_init: true)

  def type
    :jsonb
  end

  def cast(value)
    decoded = ActiveSupport::JSON.decode(value)
    decoded.map do |obj|
      obj["amount"] = amount_to_money(obj["amount"])
      DISCOUNT_LINE.new(obj)
    end
  end

  def amount_to_money(amount_hash={})
    value_cents = amount_hash['value'].to_s.to_f * 100
    return Money.new(value_cents, amount_hash['currency'])
  end

end

# order.rb
class Order < ApplicationRecord
  # discount_lines is stored in the database as a jsonb column
  attribute :discount_lines, :discount_line_type, array: true
end

# Usage
> o = Order.last
> o.discount_lines
 => 
[#<struct Order::DiscountLineType::DISCOUNT_LINE
  description="Big sale",
  name=nil,
  amount=#<Money fractional:100 currency:USD>>] 
> o.discount_lines.first.description
 => "Big sale"