The interviewer just said…
“Walk me through your domain model.”
This is the whiteboard moment. Draw nouns and one state machine. Resist adding UserProfile, Review, or PaymentGatewayConfig.
What you should do next
Draw six entities and how they connect. Narrate as you go: “A theater belongs to a city and has screens. A show is a movie playing on a screen at a time. Seat availability is per show, not per screen template.”
Entity whiteboard
┌─────────┐ ┌──────────┐ ┌────────┐
│ Movie │ │ Theater │────▶│ Screen │
│ id,name │ │ id,city │ │ seats[]│
└────┬────┘ └────┬─────┘ └───┬────┘
│ │ │
└───────┬───────┴───────────────┘
▼
┌────────┐ ┌───────────┐
│ Show │──────▶│ ShowSeat │
│ time │ 1:N │ status │
└────────┘ └───────────┘
│
▼
┌────────┐
│ Ticket │
└────────┘Field cheat sheet (matches hub/scripts/movie-ticket-sourced/)
| Entity | Key fields |
|---|---|
Movie |
id, name |
Theater |
id, name, city, screens[], shows[] |
Screen |
id, theater, seats[] — layout template only |
Show |
id, theater, screen, movie, date, time, seats[] |
ShowSeat |
showId, SeatId, status, reserveTime — live inventory |
Ticket |
id, userId, showId, seats[], paymentId |
@Builder @Data
public class ShowSeat {
String showId;
String SeatId;
SeatStatus status;
LocalDateTime reserveTime;
}ShowSeat is the object interviewers care about — one row per (showId, seatId) with mutable status.
Seat status state machine
reserveSeat() bookSeat()
AVAILABLE ──────────▶ RESERVE ──────────▶ BOOKED
▲ │
│ releaseSeat() │ (cancel / payment fail / timeout)
└────────────────────┘Enum in hub/scripts/movie-ticket-sourced/:
public enum SeatStatus {
AVAILABLE, BOOKED, RESERVE
}- AVAILABLE — anyone can select it
- RESERVE — soft hold during payment; other users must not get it
- BOOKED — confirmed; only cancel releases it
Why ShowSeat is separate from Screen seats
Common confusion: “Screen already has List<String> seats — why duplicate?”
| Screen.seats | ShowSeat |
|---|---|
| Static layout | Per-show inventory |
| Same for every show on that screen | Different status per show |
| Created when screen is built | Row per show × seat at show creation |
Tonight’s 7pm and 10pm shows on the same screen share layout but not availability. User A can book A1 for 7pm while A1 is still available at 10pm — two different ShowSeat rows (showId=sh1 vs showId=sh2).