```ruby
# An OpenBuy represents a Buy transaction on Bitex.
# OpenBuys are open buy positions that are closed by one or several CloseBuys.
# TODO: document attributes.
#
class BitexBot::OpenBuy < ActiveRecord::Base
  belongs_to :opening_flow, class_name: 'BuyOpeningFlow', foreign_key: :opening_flow_id
  belongs_to :closing_flow, class_name: 'BuyClosingFlow', foreign_key: :closing_flow_id

  scope :open, -> { where('closing_flow_id IS NULL') }
end
```

Use nested module/class definitions instead of compact style.
user
```ruby
# An OpenBuy represents a Buy transaction on Bitex.
# OpenBuys are open buy positions that are closed by one or several CloseBuys.
# TODO: document attributes.
#
module BitexBot
  class OpenBuy < ActiveRecord::Base
    belongs_to :opening_flow, class_name: 'BuyOpeningFlow', foreign_key: :opening_flow_id
    belongs_to :closing_flow, class_name: 'BuyClosingFlow', foreign_key: :closing_flow_id

    scope :open, -> { where('closing_flow_id IS NULL') }
  end
end
```
assistant