System Overview - User, Group, Expense classes
This system manages users, groups, and expenses. Users can join groups and add expenses shared among group members. The system tracks who paid and who owes money.
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User, Group, Expense classes in LLD - Architecture Diagram
Architecture Diagram
+-------+ +--------+ +---------+
| User |<----->| Group |<----->| Expense |
+-------+ +--------+ +---------+
^ ^ ^
| | |
+---------------+----------------+
|
Database
Components
User
class
Represents a person using the system with attributes like name and ID.
Group
class
Represents a collection of users who share expenses.
Expense
class
Represents a cost paid by a user that is shared among group members.
Database
database
Stores persistent data for users, groups, and expenses.
Request Flow - 4 Hops
User → Group
User → Expense
Expense → Database
Group → User
Failure Scenario
Component Fails:Database
Impact:New expenses cannot be saved; users cannot retrieve updated group or expense data.
Mitigation:Use database replication and caching to serve read requests; queue writes for retry when DB is available.
Architecture Quiz - 3 Questions
Test your understanding
Which component stores the persistent data for users, groups, and expenses?
Design Principle
This design separates concerns by modeling users, groups, and expenses as distinct classes. It uses a database for persistence and ensures communication flows logically from users to groups to expenses, supporting scalability and maintainability.