add BuyCryptoOrder and SellCryptoOrder entities

app/models/sell_crypto_order.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+# == Schema Information
+#
+# Table name: sell_crypto_orders
+#
+#  id                    :bigint           not null, primary key
+#  paid_amount           :decimal(20, 10)  default(0.0), not null
+#  received_amount_cents :integer
+#  status                :string           not null
+#  created_at            :datetime         not null
+#  updated_at            :datetime         not null
+#  currency_id           :bigint           not null
+#  user_id               :bigint           not null
+#
+# Indexes
+#
+#  index_sell_crypto_orders_on_currency_id  (currency_id)
+#  index_sell_crypto_orders_on_user_id      (user_id)
+#
+# Foreign Keys
+#
+#  fk_rails_...  (currency_id => currencies.id)
+#  fk_rails_...  (user_id => users.id)
+#
+class SellCryptoOrder < ApplicationRecord
+  include Processable
+
+  belongs_to :user
+  belongs_to :currency
+
+  monetize :received_amount_cents
+
+  validates :paid_amount, presence: true, numericality: { greater_than: 0 }
+  validates :received_amount_cents, presence: true, if: :completed?
+end