Design Restaurant Ordering (LLD)

1. Requirements

• Functional

  • Menu with categories, items, modifiers, and optional combos.
  • Orders aggregate line items; kitchen receives tickets by station (grill, cold).
  • Table or counter service flows; bill splitting optional extension.

• Non-Functional

  • Order state machine consistent when POS and kitchen display both update.
  • Extensible pricing for happy hour and coupons without dirty flags everywhere.

• Assumptions / Out of Scope

  • Delivery marketplace routing omitted; dine-in and takeaway only.

2. Core Entities

3. Class Diagram

4. State / Sequence Diagram (where relevant)

5. Design Patterns Applied

• Composite — Combo meals containing child items. Composite pattern.
• Strategy — PricingPolicy for discounts. Strategy pattern.
• Observer — Order status pushes to waiter tablets. Observer pattern.

6. Implementation

Go

package restaurant

type MenuItem struct {
    Identifier string
    Name       string
    BasePrice  int
    Station    string
}

type OrderLine struct {
    Item       MenuItem
    Quantity   int
    Modifiers  []string
}

type Order struct {
    Identifier string
    Lines      []OrderLine
    Status     string
}

type OrderService struct {
    Menu *Menu
}

func (service *OrderService) SubmitOrder(order Order) error { /* validate + emit tickets */ }

JavaScript

class Order {
  constructor({ identifier, tableId }) {
    this.identifier = identifier;
    this.tableId = tableId;
    this.lines = [];
    this.status = 'draft';
  }
  addLine({ menuItem, quantity, modifiers }) { /* ... */ }
}

class KitchenBoard {
  constructor({ stations }) {
    this.stations = stations;
  }
  receiveTickets(order) { /* partition lines by station */ }
}

7. Concurrency / Thread Safety

• Collisions: Kitchen marks ready while cashier applies void line.
• Granularity: Optimistic locking on Order version; event log for kitchen screen replay.
• Go: Mutex per order id during payment capture.

8. Extensibility & Followups

• Inventory decrement hooks when order submitted per ingredient BOM.
• Reservation system linking table turn rotation.
• Edge cases: 86 item mid-order, allergy overrides, split checks across parties.