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Companion Code Repository

From Problems to Patterns: Domain-Driven Design and Event Sourcing in .NET

From Problems to Patterns — Domain-Driven Design and Event Sourcing in .NET By Najaf A. Shaikh · First Edition, 2026

build-samples

Overview

This directory contains the complete, runnable companion code for all 32 chapters of the book. Every code example from every chapter builds and all tests pass. The code evolves chapter by chapter through a single Bank Account domain — starting from a naive CRUD implementation and ending with a containerised, observable, event-sourced system built on SourceFlow.Net v1.0.0.

How to Open

Single root solution (recommended)

Open BankAccount.sln in Visual Studio 2022 or Rider. All 28 projects from all 7 parts load in a single solution, organised into solution folders by Part.

BankAccount.sln
├── Part-I -- Thinking in Domains
│   ├── src/  BankAccount.Domain
│   └── tests/ BankAccount.Domain.Tests
├── Part-II -- Modelling with Events
│   ├── src/  BankAccount.Commands, BankAccount.Domain, BankAccount.Infrastructure
│   └── tests/ BankAccount.Tests
├── Part-III -- Commanding Change
│   ├── src/  BankAccount.Application, BankAccount.Domain, BankAccount.Infrastructure
│   └── tests/ BankAccount.Tests
├── Part-IV -- Reading the World
│   ├── src/  BankAccount.Api, BankAccount.Domain
│   └── tests/ BankAccount.Tests
├── Part-V -- Infrastructure and Persistence
│   ├── src/  BankAccount.Api, BankAccount.Domain, BankAccount.Infrastructure
│   └── tests/ BankAccount.Tests
├── Part-VI -- Production Readiness
│   ├── src/  BankAccount.Api, BankAccount.Domain, BankAccount.Infrastructure
│   └── tests/ BankAccount.Tests
└── Part-VII -- Inside the Framework
    ├── src/  BankAccount.Api, BankAccount.Domain, BankAccount.Infrastructure,
    │         BankAccount.Infrastructure.Audit, BankAccount.Infrastructure.Aws,
    │         BankAccount.Infrastructure.MongoDb
    └── tests/ BankAccount.Tests

Per-part solutions

Each part also has its own self-contained solution if you want to focus on a single part:

Part-I/Part-I.sln
Part-II/Part-II.sln
...
Part-VII/Part-VII.sln

Build and Test

# Build everything
dotnet build BankAccount.sln

# Run all 152 tests across all 7 parts
dotnet test BankAccount.sln

# Or test a single part
dotnet test Part-III/Part-III.sln

Part-by-Part Guide

Part Chapters Key Concepts Projects
I — Thinking in Domains 1–6 CRUD problems, Ubiquitous Language, Bounded Contexts, Value Objects, Aggregates, Domain Events BankAccount.Domain
II — Modelling with Events 7–11 Hand-built append-only command log, sequencing, EF Core persistence, replay, snapshots BankAccount.Domain, BankAccount.Commands, BankAccount.Infrastructure
III — Commanding Change 12–16 SourceFlow.Net adoption, Commands, Command Pipeline, Sagas, multi-step Sagas, Compensation BankAccount.Application, BankAccount.Domain, BankAccount.Infrastructure
IV — Reading the World 17–22 Event Pipeline, Read Models, Projections, Eventual Consistency, Validation, Projection Rebuild BankAccount.Api, BankAccount.Domain
V — Infrastructure & Persistence 23–26 Three-store architecture, EF Core integration, Schema Evolution, full production stack BankAccount.Api, BankAccount.Domain, BankAccount.Infrastructure
VI — Production Readiness 27–29 Polly resilience, OpenTelemetry tracing, Docker containerisation BankAccount.Api, BankAccount.Domain, BankAccount.Infrastructure
VII — Inside the Framework 30–32 Framework internals, MongoDB custom store, AWS SQS cloud dispatch BankAccount.Api, BankAccount.Domain, BankAccount.Infrastructure, .Audit, .Aws, .MongoDb

Prerequisites

  • .NET 9 SDK
  • Visual Studio 2022 v17.8+ or JetBrains Rider or VS Code with C# Dev Kit

Parts III–VII reference SourceFlow.Net via a local project reference to References/SourceFlow.Net. No NuGet restore is needed for the framework — it is included in this repository.

Parts VI and VII include Dockerfile and docker-compose.yml. Docker Desktop is required only if you intend to run the containerised deployment examples from Chapters 29–32.

Repository Layout

Code/
├── BankAccount.sln          ← Root solution — opens all 28 projects
├── Part-I/                  ← Chapters 1–6
├── Part-II/                 ← Chapters 7–11
├── Part-III/                ← Chapters 12–16
├── Part-IV/                 ← Chapters 17–22
├── Part-V/                  ← Chapters 23–26
├── Part-VI/                 ← Chapters 27–29  (includes Dockerfile)
└── Part-VII/                ← Chapters 30–32  (includes Dockerfile, MongoDB, AWS)

SourceFlow.Net

The framework used throughout Parts III–VII is SourceFlow.Net v1.0.0, included as a NuGet package reference.

See Appendix A of the book for the full SourceFlow.Net API reference, and Appendix D for dev environment setup instructions.

All code targets .NET 9. All tests use xUnit + FluentAssertions.