Build purchase abstraction

[morremeyer]

A purchase is an abstraction over multiple goods

The following shall be built:

• A purchase model with the following fields:

  • OneToMany goods
  • boolean flag is_netto (default: True)
  • status of payment
  • method of payment
  • person who payed

• A good model with the following fields:

  • name (required)
  • price in 100th cent (default: None)
  • tax rate in percent (integer, default 19)
  • OneToMany orders

The save method of a purchase shall have an optional attribute state that updates the state of all orders related to the purchase.