Vertical Slice Architecture vs Traditional Layered Architecture: Side-by-Side Code

Let's compare how the same "Create Customer" feature looks in both architectures.

Traditional Layered Approach

Files you must touch across a typical Clean Architecture solution:

• Controllers/CustomersController.cs — HTTP endpoint
• Application/Customers/CreateCustomerCommand.cs — DTO
• Application/Customers/CreateCustomerHandler.cs — business logic
• Application/Common/Interfaces/IAppDbContext.cs — abstraction
• Domain/Entities/Customer.cs — domain entity
• Infrastructure/Persistence/AppDbContext.cs — EF Core context
• Web/Program.cs — DI registration

Seven files across four projects. When a bug is reported in customer creation, you must trace the flow through all of them.

VSA Approach

One file in one folder Features/Customers/CreateCustomer.cs contains: the Minimal API endpoint, the MediatR command, the handler with all business logic, the EF Core query, and the response DTO. When a bug is reported, you open one file. When you need to add a field to customer creation, you edit one file. This is the essence of VSA: maximum cohesion, minimum scattering.

Key Takeaways

• Layered: 7 files, 4 projects. VSA: 1 file, 1 folder.
• Bug tracing: hours vs minutes
• Feature addition: touch 7 files vs touch 1 file
• All Indotalent products demonstrate this VSA pattern in production code