Modular Feature-Based Clean Architecture

1. Introduction

MFCA is a pragmatic backend architecture that combines Domain Driven Design (DDD) principles, Clean Architecture, REPR Pattern, Vertical Slice Architecture and N Layer Architecture.

2. Architectural Goals

🧩 Feature Modularity
🧠 Domain Modeling
🧪 Make unit testing easier
⚡ Less Complexity than CQRS
🚀 Scalable and Easy to Maintain

3. Project Structure

csharp_mfca.API/
├── Configurations/
├── Constants/
├── Entities/
├── Exceptions/
├── Extensions/
├── Features/
│   ├── Core/
│   ├── Users/
│   │   ├── Core/
│   │   └── CreateUser/
├── Models/
├── Middlewares/
├── Persistence/
│   ├── Base/
│   ├── Wrapper/
├── Resources/
├── Services/
├── Utils/
├── Program.cs / Dockerfile

4. Layers & Responsibilities

Layer	Responsibility
Configurations	Manages application settings efficiently using the Options Pattern, ensuring type safety and reducing the risk of spelling errors or misconfigurations across the codebase.
Constants	This is where the application constants and enum exist.
Entities	The main entities of the application if we are using one DB instance.
Exceptions	This is where we can implement custom exceptions and global handlers.
Extensions	Custom implementation of extensions including Mapper, Extension and DI extensions.
Features	Encapsulated domain features, Request DTOs, Response DTOs validators, and service calls.
Models	Domain entities used across features including aggregates.
Middlewares	Custom middlewares for interception and custom logic.
Persistence	Generic Repository Pattern, Unit Of Work Pattern lie in this layer. Also, ORM integration can be found there.
Resources	We can add localization here.
Services	Shared services like Fluent Email, JWT, AES, S3, SES, SNS, etc.
Utils	Mainly BaseResponseModel for consistent API response.

5. Testing Strategy

Unit test business logic
Validate DTOs with FluentValidation
Integration tests via controllers and DB context

6. Advantages Over CQRS

Traditional CQRS	MFCA
Two separate commands and queries	Request/Response DTOs under the slice and aggregates under the Core if needed.
Dual databases or projection layers	Single DB with layered access
Heavy setup and boilerplate	Minimal overhead, fast development

7. Extensibility

Scale individual features as needed.
Easily integrate MediatR, background jobs, etc.
Future migration to microservices possible per feature.