Domain-Driven Design

My 11/6/2007 .NET Developers Group Presentation

Tim McCarthy — Wed, 07 Nov 2007 12:50:00 GMT

Here are the slides and here is the code from my presentation yesterday. Thanks to everyone who attended, I thoroughly I enjoyed discussing my upcoming book with you guys!

By the way, here is the link to my book on the Wiley web site:

http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470147563.html

Slides and Code from my ITARC 2007 Presentation

Tim McCarthy — Tue, 16 Oct 2007 21:25:00 GMT

Here are the slides and here is the code from my presentation today. Once again, a big thank you to all who attended, you were all very helpful to me!

As I said before my book should be out in April of 2008…it sure is a lot of work doing a book all by myself :)

I am writing a book on Domain-Driven Design

Tim McCarthy — Tue, 06 Mar 2007 23:07:00 GMT

I have been talking to people about this for a while, so I figured I’d blog about it too. Actually, I promised my friends over at the Domain-Driven Design Yahoo group that I would! The full title of the book is .NET Domain-Driven Design with C#: Problem-Design-Solution, and it will be published by Wiley Publishing, Inc.

The idea behind the book is that it will be a case-study book…a real-world application that uses Domain-Driven Design (DDD) concepts. After reading other bloggers’ posts, and hearing people ask for real-world examples on the DDD Yahoo group, I have decided to write a book that addresses this exact topic. The book is due to be completed at the end of the year, and will probably be out in early 2008.

My plan is to put some of the issues I run into on this blog and/or the DDD Yahoo group and see what other people have to say about their solutions to similar problems.

A Composite Specification Pattern Implementation in .NET 2.0

Tim McCarthy — Mon, 22 Jan 2007 16:15:00 GMT

.NET 2.0 Composite Specification Pattern Implementation

According to Fowler and Evans, the idea of using Specifications is to separate the statement of how to match a candidate, from the candidate object that it is matched against. The main motivation pattern is to be able to select a list of objects from another list using various criteria in a very flexible, robust way. A nice side benefit of using Specifications is that they can be used for object validation/constraints as well as for building objects to order (like in a Factory). I was first introduced to this pattern from reading Eric Evans’ excellent book, Domain-Driven Design.

I have implemented the Specification pattern using the Composite pattern in order to provide the ability to combine Specifications in various ways. I really needed this in a project, and I was surprised that I could not find any .NET implementations out in the blogoshpere, so I went ahead and wrote my own, with a little help from Reflection and Generics.

Here is the basic diagram of the top-level classes:

For the AndSpecification and OrSpecification classes, they both take two ISpecification instances in their constructors, which represent the classes to be AND’ed or OR’ed together.

Here is a diagram of the Leaf-node classes of the Composite:

As you can see in this diagram, every Leaf is actually a Composite, which makes it very easy to combine Specifications. Below is a code example of how to combine specifications and use them:

///

///A test for IsSatisfiedBy (TCandidate)

///

[TestMethod()]

public void CustomerIsSatisfiedByEqualAndStartsWithTest()

{

TestCustomer candidate = new TestCustomer();

candidate.FirstName = "Tim";

candidate.LastName = "McCarthy";

bool expected = true;

bool actual = new EqualSpecification<TestCustomer,

string>("FirstName",

"Tim").And(new StartsWithSpecification<TestCustomer,

string>("LastName", "M")).IsSatisfiedBy(candidate);

Assert.AreEqual(expected, actual,

"The CompositeSpecification did not return the expected value.");

}

In this example, an EqualSpecification is combined with a StartsWithSpecification to perform two tests on the candidate object, which happens to be a TestCustomer type. The first test specifies that the FirstName property of the TestCustomer instance (the candidate) is equal to “Tim”. The second test specifies that the LastName property of the TestCustomer instance (the candidate) starts with the character “M”. The power of this is that the tests by themselves are very granular and easy to understand, yet also very easy to combine and execute, as evidenced by how the code sample combined two specifications on one line of code.

The code for the implementation (as well as a sample application) can be found here. Enjoy!

[5/22/2007: I moved the code for this project over to CodePlex. It can now be accessed here: http://www.codeplex.com/spec]

I definitely welcome any feedback on this code as well.

My talk on Domain Driven Design for the OC C#/VB.NET/Architecture User Groups

Tim McCarthy — Wed, 13 Dec 2006 08:51:00 GMT

First off, I have to say that I had a great audience, very intuitive and sharp! I am posting my slides and code again (even though I just gave this talk last week in San Diego) since I went through and added a bunch of stuff to it.

Here are my latest slides and code. As promised, in the code contains a full-blown .NET implementation of the Composite Specification pattern using .NET Generics.

Enjoy!

My talk on Domain Driven Design for San Diego .NET Developers Group

Tim McCarthy — Wed, 06 Dec 2006 11:34:00 GMT

That was a fun talk! Here are my slides and here is my code. As promised, here is a diagram of the latest DDD framework that I have developed: