Questions

• Are we going to write code or a class diagram is enough?
  • Code is required.
• Are we going to persist the data?
  • Yes
• How will user use the system?
  • Using GET and POST request.

Sketch

User Journey

Kinds of users

• Admin
  • Adds new city
  • Adds new theatre
• Theatre Owner
  • Adds audis to the theatre.
  • Adds shows to the theatre.
• Customer
  • Select Cities.
  • Search a Movie
  • List of theatres
  • Select theatres.
  • List of shows.
  • Select a show.
  • Select seats.
  • Make Payment
  • Get Ticket

Requirements:

• BMS will have multiple cities.
• Cities will have multiple theatre.
• Theatre will have multiple audis.
• Audis will have multiple seats.
• Each Seat will have a type.
• Audis will have available features.
• Shows will have required features.
• Shows has start and end time.
• Multiple seats can be booked with a single ticket.
• Limit number of seat allowed to be booked with 1 ticket.

Behaviours

• Status [ Available, Locked, Booked , Not available ] is a seat in a show.
• Price is related to seat type in the show.

ENUMS	CLASSES
Seat Type	Cities
Role	Theatre
Features	Audis
Seat Status	Shows
Theatre Status	Tickets
Payment Mode	Payment
Payment Status	User
	Seat
	Bill
	SeatInShow
	SeatTypeInShow

Enums

1. SeatType: Silver, Gold, Platinum
2. Role: Admin, owner, user
3. Features: 2D, 3D, DOLBY, 4D
4. SeatStatus: available, under_maintainance, locked, booked
5. TheatreStatus: open, closed
6. Payment Mode: card, netbanking
7. Payment Status: failed, successful, in-process

Classes

City
id
name
list (theatres)

Theatre
id
name
address
list (audis)
maxBookingSeatAllowed

Audis
id
name
list (Seats)
list (features)
rows
columns

seat
id
number
seatType
Row
Coloumn

User
id
list (role)
username
password

Show
id
start time
end time
audi
name
list (features)

seatInAShow
id
Seat
show
seatStatus

seatTypeInShow
id
seatType
show
price

Ticket
id
user
booking time
list (SeatInShow)
list (payment)
user

Payment
id
payementStatus
paymentProvider
amount
transaction id
ticket

Schema Design

1. Classes & enums become table.
2. Primitive Attributes should be the columns - Primitive data types. - string - date/time
3. Relationship : (1:1): any side FK, (1:M): on m side FK , (M:M): mapping table

• All enums as tables with two coloumns -> id and value

1. City : id, name
2. Theatre: id, name, address, maxSeatBookingAllowed, cityID
3. Audi: id, name, rows, coloumns, theatreId
4. User: id, name, password, username
5. Seat : id, number, row, coloumn, audiId, seatTypeId
6. Show: id, name, start_time, end_time, audiId
7. Ticket: id, booking_time, user_id
8. Payment: id, amount, transaction_id, ticket id
9. SeatInShow: id, seatIId, showId, seatStatusId
10. SeatTypeInShow: id, price, seattypeID, showId
11. AudiFeatures: id, audiId, featureId
12. UserRole: id, userId, roleId
13. ShowFeature: id, showId, featureId

Annotation

Lombock

- Getter  -> Add getter methods
- Setter -> Add the setter Methods

Model

• Entity -> For creating table
• MappedSuperClass -> to make properties part of another table
• Id -> To treat it as primary key
• GeneratedValue -> For auto increment

Relationship

• OneToMany (mappedBy="")
• ManyToOne
• OneToOne
• ManyToMany

Enums

• Enumerated -> For enums

• ElementCollection -> For list of enums

• Rather than creating dependency object and then injecting in the constructor we could use following annotations of springboot:

Dependency Injection

- Controller
- Autowired
- Service
- Repository 

Concurrency Problem

If user1 selected A1 and A2 seat at 9:05 and user2 selected A2 and A3 seats at 9:05. User 1 clicked on book ticket at 9:06 and user2 at 9:07.

Locked the seat A1 and A2 at 9:06 and dummy ticket is generated.

Flow:

1. Get showSeats of selected IDs
2. Check if they are avaialabe.
3. If not available, send back with an exception
4. else Lock them
5. Prepare dummy ticket
6. Return Ticket

Ideal Flow:

Selected Seat -> Locked -> Login -> sent to Payment Gateway -> Pay -> Success -> Redirected to BMS-> Success -> Ticket Status Booked

- What will be added in the the dummy ticket and when? Select (ShowSeatId) -> Login (UserId) -> Pay (PaymentId)

Payment	Redirection	Status
Success	Success	Booked
Success	Failed	Locked and Refund should be initiated
Failed	Success	Not Booked and locked
Failed	Failed	Locked

• Locked should be considered available after 6 minutes.
• Locked : Now - lockedAt < 6 minutes -> locked else consider it available.

If redirection succeed, then BMS knows what to do and what actually happened.

Refunds

• Reconciliation
  • BookMyShow and Payment Gateway maintains files at their end for all the entries.
  • Files are compared get the difference (Breaks).
  • Refund needs to be initiated.
  • External Breaks: External party have additional entries.

Transaction

SET TRANSACTION ISOLATION LEVEL SERIALISABLE

• Read with lock (Select for update)

• Check in App

• Update

• ORM

• Pessimistic Read/Write

• Different types of locks in Transactional