<strong>Separation of concerns</strong> is organizing code so that each part handles one specific responsibility. It makes code easier to understand, test, and maintain by avoiding mixing unrelated logic.
The Kitchen Organization Analogy
Kitchens separate prep, cooking, and plating. Each station has one job. Code should work the same—separate data, logic, and presentation.
Prep Station (Data Layer)
Handle ingredients
Cooking Station (Business Logic)
Prepare dishes
Plating Station (Presentation)
Serve beautifully
Database Access
Core Functionality
UI/API
Identify concerns
Data access, business rules, UI, validation
Create separate modules
UserRepository, UserService, UserController
Define clear interfaces
Each layer exposes clean API
Avoid mixing concerns
Don't put SQL in UI code
Test independently
Test business logic without database
Wrong
"More layers = better separation"
Correct
<strong>Balance separation with simplicity</strong>. Don't over-engineer. For small apps, 3 layers (data, logic, presentation) are enough. Add layers only when needed.
User registration:
Bad: All in one function (validation + DB + email + logging)
Good: UserValidator, UserRepository, EmailService, Logger
Each class has one job, easy to test and modify
Change email provider? Only update EmailService
Add logging? Inject Logger, don't modify other code