Juan Vazquez said
This is a great book to get up to speed on Java's ruby on rails clone. It is well written, which made it a quick read. Grails is quickly evolving and the latest version may require some minor tweaks to the examples presented. This is a must have for those getting started with Grails.

Jacek Laskowski said
The Definitive Guide to Grails, Second Edition (aka DGG2) is no doubt the best Java book I've ever read, and for what it's worth mentioning I read it from cover to cover. It was not only because it was about Grails I meant to get skilled at, but also for its comprehensive English language. I took the liberty of writing complete reviews of each chapter on my blog, so it kept me busy almost 3 months to digest all the Grails goodies Graeme and James collected in their book. Although it was my second book about Grails (after "Beginning Groovy and Grails: From Novice to Professional") I couldn't stop reading it. The more I read the often I asked myself why it took me so long to appreciate Grails features. The book covers the features of Grails 1.1 which was in beta while the book was written yet the material didn't get outdated with its final release. The authors made all the efforts to ensure the book is complete and up-to-date even though Grails 1.1 was not available at that time yet.

I don't want to spoil your reading of the book and its unique style of explaining Grails features by its authors, so if you're like me chasing the simplicity of Grails and trying it out in your projects that's definitely a book you have to read. There are almost 650 pages divided into 17 chapters and one appendix about Groovy - the language of Grails. You shouldn't afford yourself just to read it once - you might easily fail to notice all the gems presented in this book. There are so many that even reading it twice might not be enough. I had a pleasure to read it once, underline all the stuff I considered useful and used it in the reviews afterwards. All in all I think I read it a couple of times and I always found something new I'd missed earlier. I must admit that after a few weeks I was even completely fed up with Grails as there were too much to digest. It reminded me of reading a science book with lots of equations, examples and their explanations - even if I enjoyed it and could read it over night, the best bet to not get swamped was to read it chapter by chapter or even section by section and do the samples myself. DGG2 was not different. It contains the gory details of Grails presented by its project lead and its project member, so who else could bring you the latest stuff right and in details?

It's definitely a definitive guide to Grails. I don't think Grails could have been presented better than what you can find in the book. I'm sure many could share my view that one can't call himself a Grails expert unless (s)he has read the book. You can't simply let yourself miss the pleasure of reading the book. It's like you never programmed with Java IDE and be once presented with its features one by one in a very organized manner. You'll surely get astonished how much you missed for so long. So will happen to you after reading this book. No matter whether you're a Grails developer now or want to become one soon, you'll come across many ground-breaking solutions of Grails in this book. It is highly recommended for anyone who keeps looking for the Holy Grail of the web application frameworks. It could just be Grails after all.

Trevor Burnham said
This is one of the best-written programming books I've come across. It covers every aspect of creating a Grails application. Although this is a thick book, and not a "put together a Grails app in a few hours" book, it nonetheless manages to keep a brisk pace, conveying plenty of useful information without getting mired in detail.

As a bonus, the book features an appendix that covers the basics of the Groovy programming language. However, if you plan to develop in Groovy on a regular basis, you might want to consider adding Groovy in Action to your library.

[Edit: Grails 1.1 has been released since this book came out. The changes to the API are pretty minor, so this book still stands out as an excellent introduction. However, Grails in Action (which I haven't read yet) promises to be a more up-to-date primer.]

Cedric Dandoy said
I already had the first edition of this book and upgraded to the second edition because of the 250 additional pages.
My team is working on a Grails application and this book helped me/us a lot.
Both Grails and this book deserve the 5 starts.

M. Fromin said
I started to read this book on a business trip. As such I made it to Chapter 6 without turning on a computer. Having a background in Rails I found many similarities with the added benefit of a tighter integration to Java. Both of these facts were positives to me.

However, when I returned home and attempted to work through the examples I could not get through Chapter 2's simple scaffolding examples.

The scaffolding did not work as described in the book and to add to the excitement, the test created for StoreController in Chapter 1 (yeah - Ch.1) inherits from a different class than the one shown in the book (GrailsUnitTestCase in beta as opposed to ControllerUnitTestCase in the book).

(update) I was eventually able to make Ch 1 and 2 work after some time hunting around the Grails mailing list archives on Nabble. Seems that scaffolding has been through some changes in 1.0.4 / 1.1 and the Grails team is addressing.

If you want to see where Grails 1.1 is heading this may be a good book but until Grails goes "final" and we get updated code examples I would tred carefully with this book.