I must admit that when I first heard of the Domain-Driven Design in PHP initiative, I was a bit worried. The danger was twofold: first of all, when glancing over the table of contents, the subject matter looked like it was a rehash of content that was already available in several other Domain-Driven Design books. Second, writing a book on Domain-Driven Design targeted specifically toward the PHP community seemed needlessly narrowing, particularly as Domain-Driven Design itself is not language specific. As such, this might inhibit PHP developers from looking past the boundaries of their own community, especially when considering that there's a lot going on beyond the scope of PHP. In fact, even Domain-Driven Design is one of those things, as it didn't originate in the PHP community.

After reading the book, I'm happy to inform you that my worries have been invalidated!

With regard to my first concern: of course there is some overlap with previously published Domain-Driven Design books. Yet the authors have restrained themselves. The theoretical parts are exactly what you need to be able to understand what's going on in the code samples. Besides, if you never read another Domain-Driven Design book, this one gives you what you need to start applying some Domain-Driven Design principles and patterns in your code, as it's practical by nature.

My second concern — about the PHP aspect of this book — has been addressed very well. It turns out there are a lot of things to say about Domain-Driven Design in a PHP world. This book is specifically targeted at an audience consisting of PHP developers. The code samples resemble real-world PHP projects, and the authors use a programming style we know from projects using Symfony or Silex. For persisting Domain objects, Doctrine ORM — which is the de facto standard data mapper for PHP — is used.

This book also fulfills a need I've often seen in the PHP community: the need for concrete examples. It's not always easy for authors to come up with proper illustrations of how to apply certain ideas that have a low risk of being misinterpreted or abused in real-world projects. And in Domain-Driven Design, which is philosophical by nature, this is even more challenging.

In the case of this book, the authors haven't been afraid to show many useful examples, along with some interesting alternative solutions. They aren't just handwaving at solutions either; they take the time to provide detailed explanations — such as when they talk about saving snapshots for Aggregates with a large number of Domain Events, or when they discuss integrating Bounded Contexts using RabbitMQ. I can't recall having previously seen an implementation of these things in a book or article on Domain-Driven Design.

For me personally, Domain-Driven Design is one the most interesting subjects in software development today. There is so much to discover, and there are many subjects related to it: Agile software development, TDD, and BDD, but also living documentation, visualization, and knowledge crunching techniques. Once you start looking into all of this, you'll realize that Domain-Driven Design is an area of expertise worth investigating, as it enables you to add much more to your own worth as a software developer.

So, I guess what I want to say is this: dive into this book, learn from it, and then pick up another book (see the list of references at the end of this book for suggestions of future reading). Continuous learning is a fundamental part of keeping up to date in the software industry, so don't stop here.

Oh, and by the way: if you get a chance to go to Barcelona, make sure you take part in one of the many PHP or Symfony events. The community is big, friendly, and full of interesting ideas. You'll find the authors of this book there too. They are all invested in the local PHP community and are happy to share their insights and experiences with you!

Matthias Noback
Author of A Year with Symfony