Interview: Greg Young Discusses State Transitions in Domain-Driven Design and DDD Best Practices

by Srini Penchikala on Jan 30, 2009 | NOTICE: The next QCon is in New York Jun 10-14, Join us!

In this interview recorded at QCon San Francisco 2008 conference, Greg Young talked about how his team has been using Domain-Driven Design (DDD) concepts in their projects. He discussed how to manage domain state transitions in a Domain-Driven Design project using two different design models, one for reading data from datastore and the other for write-only command operations. He also talked about Command Query Separation (CQS) design concept to keep design cleaner and easier to test and maintain and the best practices that developers can use when working on DDD projects.

Watch: Greg Young Discusses State Transitions in Domain-Driven Design and DDD Best Practices (36 min.)

In the interview, Greg covered the following topics:

State Transition in the Domain Model
Role of Dependency Injection (DI) and Aspect-Oriented Programming (AOP) in Domain-Driven Design
Domain Object Validation
Domain-Driven Design in .NET world
Event Stream Processing (ESP) in DDD

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Community comments

Greg Young on DDD by Ryan Riley Posted

Re: Greg Young on DDD by Robin Howlett Posted

Greg Young on DDD by Jean-Christophe Grégoire Posted

Holy heck by Raoul Duke Posted

What about in memory edits? by Ian Jones Posted

Re: What about in memory edits? by Peng Sunny Posted

Check this out as well by Nicholas Sterling Posted

Re: Check this out as well by Nicholas Sterling Posted

Greg Young on DDD by Ryan Riley

Great interview! A lot of what Greg said really resonates with a lot of things I've been trying to do, and his statements certainly cleared up some thoughts I was having on a) immutability, b) AOP, and c) the use of DTOs.

Thanks!

Re: Greg Young on DDD by Robin Howlett

This is a superb video; I have to admit viewing this interview I had very limited knowledge about DDD, but Greg succinctly and clearly outlined his understanding and expertise. The concepts outlined are of immense value - great job.

Greg Young on DDD by Jean-Christophe Grégoire

Great interview !!

Holy heck by Raoul Duke

What a wonderful interview. It is so rare to come across people who can clearly state what is obviously (in retrospect) true and useful. I kinda hate all things financial, but judging by this interview I'd happily go to work for them. We surely need more of this kind of intelligence.

What about in memory edits? by Ian Jones

When using CQS in domain driven design how would you query changes made to the domain object when the domain object changes are not persisted to the database and are only in memory? i.e. I want to make a change to a customer address, I issue a command to the customer domain object, I save the customer domain object to session. I then want to update the screen with the changes. Only later when the user is happy with the total of the changes do they commit the data to the database.
A couple of possible solutions I can think of is to have a session repository, or a way of getting a query object from the domain object.
Or does CQS not apply to this type of scenario?

What about in memory edits? by Ian Jones

stackoverflow.com/questions/1476886/how-to-impl...

Re: What about in memory edits? by Peng Sunny

JdonFramework is a DDD framework , it supports model in memory, and CQRS domain events + Asynchronous, more details jdon.dev.java.net/

Check this out as well by Nicholas Sterling

At Scala Days 2011, Erik Rozendaal gave a presentation on "Exploring light-weight event sourcing" that makes it sound quite approachable in Scala. Perhaps it is applicable for smaller projects than one should consider DDD for? The video is not available yet, but the presentation slides are:
days2011.scala-lang.org/node/138/301

Re: Check this out as well by Nicholas Sterling

Another (more polished?) version of the same talk: www.slideshare.net/dlrozendaal/exploring-lightw...