Applied Domain-Driven Design in .NET

What is Domain Driven Design (DDD) really about? How might Command Query Responsibility Segregation (CQRS) help us to build better software? Far from being esoteric concepts, they can be harnessed by everyday developers to create long-lasting, flexible solutions.

DDD and CQRS are gaining in popularity because they attack genuine challenges in software development. This course balances explaining important underlying theory with both design- and code-focused exercises, giving participants both understanding and new practical development skills. 

Rather than teaching a framework, the course teaches a factoring and some ways to implement it, highlighting the key pitfalls to avoid along the way. During the course, a small application will gradually be built up from scratch. The course also includes coverage of testing, how to apply the insights from the course to existing systems and how to scale out a system developed using CQRS. Read more about CQRS and DDD on the CQRS FAQ


.NET developers 


A good working knowledge of the C# language, including classes, interfaces and generics
Basic knowledge of SQL
Some basic experience with NUnit is beneficial, but not essential

Course outline:

The Challenge of "Database Driven" Software Development

  • Types of complexity
  • Scaling and consistency
  • Testing
  • Integration


Introduction to Domain Driven Design

  • Domains and Domain Models
  • Ubiquitous Language
  • Exercise on building a domain model


Bounded Contexts

  • Why boundaries matter
  • Context Maps
  • Decomposition in the domain
  • Composition in the UI
  • Exercises on boundary hunting


Commands, Queries and Events

  • Normalization and denormalization
  • Write models and read models
  • Events as the write-side/read-side
  • link
  • Eventual consistency and its
  • consequences
  • Designing commands
  • Designing queries
  • Exercise on command and query design


Message Busses

  • Messages as decoupling
  • Publish/Subscribe
  • Send vs. Publish
  • Building a simple message bus
  • Exercise on message bus implementation


Write Side Architecture

  • Command handlers
  • State sourcing vs. event sourcing
  • Introduction to aggregates
  • Building up aggregates from past events
  • Transactional safety
  • Exercise on command handlers and aggregates

BDD Style Testing

  • Introduction to BDD
  • Commands, Events and BDD
  • Building a simple test framework
  • Exercise on BDD


Event Stores

  • Existing options
  • Building an event store on top of an RDBMS
  • Implementing a repository using an event store
  • Advantages of freeing aggregate representation from persistence
  • Optimizations using snapshots
  • Exercise on building an event store


Advanced Aggregate Design

  • Finding aggregate boundaries
  • Coping with relationships
  • Exercise on aggregate design


Building Read Sides

  • Overall approach
  • Relational DB read sides
  • NoSQL read sides
  • Other options
  • Re-building and introducing new read sides
  • Exercise on building read sides


  • What is a saga?
  • Different types of saga
  • Handling saga state
  • Building a simple saga framework
  • Exercise on sagas


Evolving a System

  • Refining domain models
  • Handling changes to commands
  • Event versioning
  • Handling event upgrade
  • Exercise on event upgrading


CQRS, DDD and Existing Codebases

  • Introducing bounded contexts to existing systems
  • Separating commands and queries
  • Migrating towards event sourcing


Scaling out

  • Using the read/write separation to scale
  • Scaling write sides by bounded context and by aggregate
  • Scaling within an aggregate
  • Message distribution and reliability
  • Message queues and ESBs


Other Opportunities

  • Parallel development and outsourcing
  • Recreating previous states for debugging

Other relevant courses

24. September
4 days
Classroom Virtual On Demand