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Many developers make a common mistake. They put everything in the controller.
If the code works, they leave it there.
At first, this works fine. Your project is small. Your files are short.
Then the project grows. A 20-line controller becomes 100 lines. Then 300. Soon, you have 600 lines in one file.
Large controllers cause problems:
- Reading code takes too long.
- Finding bugs is difficult.
- Testing is hard.
- Changes feel risky.
You need a service layer to fix this.
A service layer handles business logic. Think of a restaurant.
The controller is the waiter. The waiter takes your order and brings your food. The waiter does not cook the food.
The service layer is the kitchen. The kitchen does the actual work.
Use this structure:
- Routes decide which endpoint to call.
- Controllers handle HTTP requests and responses.
- Services handle the business logic.
Business logic includes:
- Database queries.
- Validation rules.
- Permission checks.
- Payment processing.
Move these tasks out of your controller and into service files. This keeps controllers small. It makes your logic easy to reuse and test.
Follow these rules for clean code:
- Controllers handle the request-response cycle.
- Services handle the logic.
- Services should not use HTTP objects like req or res.
- Services throw errors.
- Controllers catch errors and return status codes.
You do not need complex architecture for small apps. Use simple controllers when you start. Switch to services as your app grows.
Separate your responsibilities. Keep your controllers small. This prevents 600-line files that nobody wants to maintain.