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

Audience:

.NET developers 

Prerequisites:

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
  • Sagas

    • 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

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