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LLDsystem_design~12 mins

Why SOLID principles guide maintainable design in LLD - Architecture Impact

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System Overview - Why SOLID principles guide maintainable design

This system demonstrates how applying SOLID principles leads to a maintainable software design. It shows components designed with single responsibilities, open for extension but closed for modification, and loosely coupled to ease changes and testing.

Architecture Diagram
  User
   |
   v
+----------------+
|  Controller    |
+----------------+
        |
        v
+----------------+       +----------------+
|  Service A     |<----->|  Service B     |
+----------------+       +----------------+
        |                        |
        v                        v
+----------------+       +----------------+
| Repository A   |       | Repository B   |
+----------------+       +----------------+
        |                        |
        v                        v
+----------------+       +----------------+
| Database A     |       | Database B     |
+----------------+       +----------------+
Components
User
actor
Initiates requests to the system
Controller
service
Handles user input and delegates to services
Service A
service
Implements business logic for feature A, follows single responsibility
Service B
service
Implements business logic for feature B, designed for open/closed principle
Repository A
repository
Handles data access for feature A, abstracts database details
Repository B
repository
Handles data access for feature B, supports interface segregation
Database A
database
Stores persistent data for feature A
Database B
database
Stores persistent data for feature B
Request Flow - 8 Hops
User → Controller
Controller → Service A
Service A → Repository A
Repository A → Database A
Database A → Repository A
Repository A → Service A
Service A → Controller
Controller → User
Failure Scenario
Component Fails:Repository A
Impact:Service A cannot access data, causing feature A to fail while other features remain unaffected
Mitigation:Use interface segregation and dependency injection to swap Repository A with a mock or fallback implementation to maintain partial functionality
Architecture Quiz - 3 Questions
Test your understanding
Which component is responsible for handling user input and delegating tasks?
AController
BService A
CRepository A
DDatabase A
Design Principle
Applying SOLID principles creates components with clear responsibilities and loose coupling. This makes the system easier to maintain, extend, and test because changes in one part do not ripple unnecessarily to others.