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LLDsystem_design~12 mins

Restaurant, Menu, Order classes in LLD - Architecture Diagram

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System Overview - Restaurant, Menu, Order classes

This system models a restaurant's core operations. It manages the menu items available and processes customer orders. Key requirements include maintaining an up-to-date menu, accepting orders, and tracking order status.

Architecture Diagram
User
  |
  v
Order Service
  |
  v
Menu Service <--> Menu Database
  |
  v
Order Database
Components
User
actor
Customer who browses menu and places orders
Order Service
service
Handles order creation, updates, and status tracking
Menu Service
service
Manages menu items and availability
Menu Database
database
Stores menu item details and prices
Order Database
database
Stores order details and statuses
Request Flow - 10 Hops
User → Order Service
Order Service → Menu Service
Menu Service → Menu Database
Menu Database → Menu Service
Menu Service → Order Service
Order Service → User
User → Order Service
Order Service → Order Database
Order Database → Order Service
Order Service → User
Failure Scenario
Component Fails:Menu Database
Impact:Menu data cannot be retrieved, so users cannot view or place orders based on current menu
Mitigation:Use caching in Menu Service to serve last known menu; alert admins to fix database; degrade gracefully by showing cached menu
Architecture Quiz - 3 Questions
Test your understanding
Which component directly stores the order details?
AOrder Database
BMenu Service
COrder Service
DMenu Database
Design Principle
This design separates concerns by having distinct services for menu management and order processing. It uses databases specialized for their data types and includes caching to improve availability and performance.

Practice

(1/5)
1. Which class should primarily hold the list of available food items and their prices in a restaurant system?
easy
A. Restaurant
B. Menu
C. Order
D. Customer

Solution

  1. Step 1: Understand the role of Menu class

    The Menu class is designed to store food items and their prices, acting as the restaurant's catalog.

  2. Step 2: Differentiate from other classes

    Order tracks customer requests, Restaurant manages overall operations, Customer represents the diner. Only Menu holds items and prices.

  3. Final Answer:

    Menu -> Option B

  4. Quick Check:

    Menu = items and prices [OK]
Hint: Menu holds items and prices, not orders or customers [OK]
Common Mistakes:
  • Confusing Order with Menu
  • Thinking Restaurant holds item prices
  • Assuming Customer stores menu data
2. Which of the following is the correct way to add a new item to the Menu class in a typical object-oriented design?
easy
A. menu.addItem('Pizza', 12.99)
B. Menu.add('Pizza', 12.99)
C. menu.insertItem('Pizza', 12.99)
D. addItem(menu, 'Pizza', 12.99)

Solution

  1. Step 1: Identify instance method usage

    Adding an item to a Menu instance uses the instance method, so calling menu.addItem(...) is correct.

  2. Step 2: Eliminate incorrect syntax

    Menu.add(...) suggests a static method which is unlikely; insertItem is not standard; addItem(menu, ...) is procedural, not OOP style.

  3. Final Answer:

    menu.addItem('Pizza', 12.99) -> Option A

  4. Quick Check:

    Instance method call = menu.addItem(...) [OK]
Hint: Use instance.method() to add items, not static or procedural calls [OK]
Common Mistakes:
  • Using static method call instead of instance method
  • Confusing method names
  • Calling functions outside class context
3. Given the following code snippet, what will be the total cost of the order?
menu = Menu()
menu.addItem('Burger', 5.0)
menu.addItem('Fries', 2.5)
order = Order(menu)
order.addItem('Burger', 2)
order.addItem('Fries', 3)
total = order.calculateTotal()
medium
A. 17.5
B. 15.0
C. 20.0
D. 12.5

Solution

  1. Step 1: Calculate cost for each item

    Burger price is 5.0, quantity 2 -> 5.0 * 2 = 10.0; Fries price is 2.5, quantity 3 -> 2.5 * 3 = 7.5.

  2. Step 2: Sum the costs

    Total cost = 10.0 + 7.5 = 17.5.

  3. Final Answer:

    17.5 -> Option A

  4. Quick Check:

    (5*2)+(2.5*3) = 17.5 [OK]
Hint: Multiply price by quantity, then add all items [OK]
Common Mistakes:
  • Adding quantities instead of multiplying by price
  • Forgetting to multiply price by quantity
  • Mixing up item prices
4. In a system where the Order class adds items without checking the Menu, what is the main issue that can occur?
medium
A. Order will reject all items by default
B. Menu prices will automatically update in Order
C. Order may include items not available in the Menu
D. Restaurant will close automatically

Solution

  1. Step 1: Understand the role of validation

    Order should verify items exist in Menu to avoid invalid orders.

  2. Step 2: Identify consequence of missing check

    Without checking, Order can contain items not on Menu, causing errors or confusion.

  3. Final Answer:

    Order may include items not available in the Menu -> Option C

  4. Quick Check:

    Missing validation = invalid items in Order [OK]
Hint: Always check Menu before adding items to Order [OK]
Common Mistakes:
  • Assuming automatic price updates
  • Thinking Order rejects items by default
  • Confusing system behavior with unrelated effects
5. How would you design the Order class to handle multiple orders from different customers simultaneously in a scalable restaurant system?
hard
A. Store all orders in a single list without identifiers
B. Keep orders only in memory without persistence
C. Allow only one order at a time to avoid conflicts
D. Use unique order IDs and store orders in a centralized database with concurrency control

Solution

  1. Step 1: Identify need for unique order tracking

    Each order must have a unique ID to distinguish between multiple customers' orders.

  2. Step 2: Ensure scalability and data integrity

    Storing orders in a centralized database with concurrency control allows multiple orders simultaneously without conflicts.

  3. Final Answer:

    Use unique order IDs and store orders in a centralized database with concurrency control -> Option D

  4. Quick Check:

    Unique IDs + concurrency = scalable order handling [OK]
Hint: Use unique IDs and concurrency-safe storage for multiple orders [OK]
Common Mistakes:
  • Ignoring concurrency issues
  • Using single list causing data overwrite
  • Not persisting orders leads to data loss