Maintaining clean code, separation of concerns, and scalability become more crucial as software programs expand. N-Layer Architecture, which divides an application into discrete layers, each in charge of a particular set of duties, is one of the most popular architectural patterns in enterprise.NET applications.
Using C#, Entity Framework Core, Repository Pattern, and Service Layer Architecture, we will construct a Vehicle Rental Management System in this post. The project’s organized N-Layer methodology enhances code organization, testability, and maintainability.
The implementation includes:
- Entity Framework Core with SQL Server
- Repository Pattern
- Service Layer
- Session Management
- Authentication and Registration
- Email Notifications
- Vehicle Rental Operations
- Console-Based User Interface
- Result Wrapper Pattern
The project demonstrates how enterprise-level architecture can be implemented even in a console application.
What Is N-Layer Architecture?
N-Layer Architecture divides an application into multiple logical layers.
Presentation Layer
Responsible for user interaction.
Examples:
- Console UI
- ASP.NET MVC
- Blazor
- WinForms
Business Logic Layer (BLL)
Contains business rules and validations.
Examples:
- Authentication rules
- Vehicle rental policies
- Customer validations
Data Access Layer (DAL)
Handles database operations.
Examples:
- Entity Framework Core
- Repository classes
- Database Context
Shared Layer
Contains reusable components.
Examples:
- Enums
- DTOs
- Utility classes
- Result wrappers
Project Structure
Required NuGet Packages
Install the following packages before starting the project:
For reading configuration from appsettings.json:
Additional console UI packages:
These packages are used throughout the application setup.
Configuring Entity Framework Core
After installing packages, create migrations and update the database.
Creating the Database Context
The AppDbContext acts as the bridge between Entity Framework Core and SQL Server.
DbSets
The application contains the following entities:
The context loads the connection string from appsettings.json and configures SQL Server using Entity Framework Core. It also defines relationships between:
- User and Customer
- Customer and Rental
- Vehicle and Rental
The project additionally uses seed data to insert default users and vehicles during database creation.
Database Configuration
The SQL Server connection string is stored in appsettings.json.
This approach keeps database configuration separate from application code.
Implementing the Repository Pattern
The Repository Pattern acts as an abstraction layer between the Business Layer and the database.
Benefits include:
- Cleaner code
- Easier testing
- Better maintainability
- Reduced database coupling
Instead of accessing Entity Framework directly inside services, repositories handle all CRUD operations.
Typical repositories include:
- UserRepository
- CustomerRepository
- VehicleRepository
- RentalRepository
Implementing the Service Layer
The Service Layer contains all business logic.
Examples include:
- Login validation
- User registration
- Vehicle rental rules
- Rental return logic
- Email notification handling
Services interact with repositories rather than directly communicating with the database.
Authentication Service
The AuthServices class handles:
- User login
- User registration
- Email validation
- Password validation
- Session creation
The service uses dependency-based communication with repositories to perform user-related operations.
Session Management
The application maintains the logged-in user using a static Session Manager.
Features
- Login
- Logout
- Current User Tracking
- Role Checking
This allows role-based navigation throughout the application.
Input Validation
Validation is centralized inside a utility class.
Email Validation
The application validates email addresses using regular expressions.
Password Validation
Passwords are checked before registration and login.
Benefits:
- Reusable validation logic
- Cleaner service classes
- Consistent validation rules
Implementing Email Notifications
The system includes an Email Sender service using SMTP.
Features
- Registration notifications
- OTP notifications
- Rental confirmations
- Future email integrations
The implementation uses Gmail SMTP for sending emails.
Result Wrapper Pattern
Instead of returning primitive values, the application uses a generic Result Wrapper.
Benefits:
- Consistent API responses
- Better error handling
- Easier debugging
- Strongly typed responses
Vehicle Rental Business Rules
The Vehicle Rental Service contains business validations before creating rentals.
Rules Implemented
- Rental period must be between 1 and 30 days
- Customer must exist
- Vehicle must exist
- Vehicle must be available
- Maximum 2 active rentals per customer
- Same vehicle cannot be rented twice simultaneously
These validations ensure business consistency before a rental is created.
Vehicle Return Process
When a customer returns a vehicle:
- Rental status is verified.
- Return date is recorded.
- Rental status changes to Returned.
- Vehicle availability is increased.
- Database records are updated.
This logic is encapsulated inside the User Service layer.
Console User Interface
The application uses Spectre.Console to create an interactive console experience.
Public Menu
Available before login:
- Login
- Register
- Quit
Administrator Menu
Available after admin login:
- View Active Subscriptions
- View Paused Subscriptions
- Logout
Customer Menu
Available after customer login:
- View Available Plans
- Subscribe to a Plan
- Pause Subscription
- Resume Subscription
- Cancel Subscription
- Logout
The menu-driven structure provides a clean user experience inside the console environment.
Advantages of Repository and Service Pattern
Separation of Concerns
Each layer handles a specific responsibility.
Maintainability
Business rules remain isolated from database logic.
Scalability
Additional features can be added without modifying existing layers.
Testability
Repositories and services can be mocked during unit testing.
Reusability
Business logic can be reused across multiple UI layers.
Best Practices Followed
- N-Layer Architecture
- Repository Pattern
- Service Layer Pattern
- Entity Framework Core
- Configuration Management
- Centralized Validation
- Session Management
- Generic Result Wrapper
- Dependency-Based Design
- Database Seeding
Conclusion
One of the best approaches for structuring medium- and large-scale C# applications is still N-Layer Architecture. Developers may build applications that are simpler to manage, expand, and test by integrating Entity Framework Core, Repository Pattern, Service Layer, and Utility Components.
This article’s Vehicle Rental Management System demonstrates how these architectural concepts interact in a practical setting. Despite the console-based nature of the application, the same architecture may be readily expanded to Blazor projects, MVC apps, ASP.NET Core Web APIs, or corporate solutions.
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