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workshop4-conference_booking.md

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Event-sourcing : conference booking

Goal: implement an event sourced complex business process (conference booking system)

Understand the business

The business we are to implement is a conference booking system. When the customer orders a seat booking for a conference, he should pay the conference price and receive a seat booking number.

Check out the following scenario:

Scenario: successfully book a seat for a conference

Given I am a customer
And I credit my account with 50E
And "Why testing is not an option" is a 50 seats conference costing 10E 
When I book a seat for the conference "Why testing is not an option"
Then my account is debited of 10E
And I get a seat booked
And available seats for conference drop down to 49

Scenario: booking attempt failure for a fully booked conference

Given I am a customer
And "Why testing is not an option" is a 50 seats conference with 50 seats already booked
When I try to book a seat for the conference "Why testing is not an option"
Then I get no seat
And my account is not debited

Scenario: booking attempt failure for a conference when the price is too high

Given I am a customer
And I credit my account with 50E
And "become master of the world in 10 lessons" is a 50 seats conference costing 1000E 
When I try to book a seat for the conference "become master of the world in 10 lessons"
Then I get no seat
And my account is not debited

Implementation

Aggregates

We have 3 aggregates

Conference

A Conference described a planned conference, with its booking state. It has the following properties:

  • the number of seats
  • the currently booked seats (indeed rather, remaining available seats)
  • the price of a seat

It's an event sourced entity, with the following states and business events: Conference workflow

Implement the missing decision/evolutions function of the entity. ConferenceTest should pass green !

Account

An Account is a user account, with its current balance in euro.

It's an event sourced entity, with only one "state" and the following business events: account workflow

Implement the missing decision/evolutions function of the entity. AccountTest should pass green !

Order

An Order represent the order passed by a customer, for a given conference. It has the following properties:

  • the name of the target conference
  • the booked seat number
  • the account Id of the customer
  • the reference of payment.

It's also an event sourced entity, with the following states and business events: Order workflow

Implement the missing decision/evolution functions of the entity.

OrderTest should pass green !

The booking process

The ConferenceBookingProcessManager is the process manager driving a conference booking requested by a user. It is supposed to:

  • check the remaining seats for the conference.
  • accept the request if the account balance of the customer is enough.
  • keep consistency between the customer booked seat, and the conference remaining available seats.
  • debit the customer account.

Implement in the ConferenceBookingProcessManager and previous 3 aggregates the process for a successful booking: Successful_booking workflow The test ConferenceBookingTest.should_book_a_seat_successfully() should pass green.

Then implement the case of a failing booking when the conference is already full: booking failed workflow The test ConferenceBookingTest.should_cancel_booking_if_the_is_place_no_more() should pass green.

Then implement the case of a failing booking when the account has not enough funds: booking failed workflow The test ConferenceBookingTest.should_cancel_booking_if_funds_are_insufficient() should pass green.