Vertical Slice Architecture

Core Principles

Organise by feature, not layer. Code that changes together lives together. A slice contains everything for a single use case.

Maintain Clean Architecture boundaries. Domain and infrastructure remain in their own layers. Slices depend inward on domain.

Isolate slices from each other. No direct slice-to-slice references. Use domain events or go through domain layer.

Keep transport layers thin. Endpoints initialise command/query, dispatch, transform result. No business logic.

Project Structure

code

src/
├── Features/                        # Vertical slices by feature area
│   ├── Rates/
│   │   ├── CreateRate/
│   │   │   ├── CreateRateCommand.cs
│   │   │   ├── CreateRateHandler.cs
│   │   │   ├── CreateRateValidator.cs
│   │   │   └── CreateRateEndpoint.cs
│   │   └── GetRate/
│   │       ├── GetRateQuery.cs
│   │       ├── GetRateHandler.cs
│   │       ├── GetRateResponse.cs
│   │       └── GetRateEndpoint.cs
├── Domain/                          # Entities, value objects, domain services
└── Infrastructure/                  # Persistence, external services

Quick Reference

Component	Purpose	Location
Command/Query	Request object	`Features/{Area}/{Operation}/`
Handler	Business logic	Same slice folder
Validator	Structural validation	Same slice folder
Response	Query DTO	Same slice folder (not shared)
Endpoint	HTTP thin layer	Same slice folder
Read Store	Query projections	`Infrastructure/ReadStores/`

Key Conventions

•Commands: ICommand or ICommand<T>; queries: IQuery<T>
•All handlers return Result<T> (FluentResults)
•Inject ISender, not IMediator
•Response DTOs co-located and not shared across slices
•Validators: structural only; business rules in handlers

Detailed References

Slice Components: See reference/slice-components.md for full code examples.

Code Review Checklist: See reference/code-review-checklist.md for VSA-specific review criteria.

When to Create a New Slice

Create when adding a new use case with distinct input/output.

Don't create when adding minor variation (extend existing) or shared utilities (use appropriate layer).

Cross-Slice Communication

Never import handlers, commands, or responses from other slices. Instead: domain layer, domain events, MediatR notifications, or direct database query (read-only).