The Definitive Guide to Grails is an introductory book to the Grails web application framework. Being an introductory book does not mean that it is only suitable for Grails beginners. Even for more experienced Grails users this book is an invaluable resource. It is written by Grails project lead Graeme Rocher and contributor Jeff Brown, who are both with SpringSource.
The first few chapters (1-7) are dedicated to explaining the basic concepts of Grails: Controllers, Views, Domain Models, Internationalization. Even tough advanced users could easily skip them, they should really skim these chapters as they not only recapture the essentials of Grails in a very intuitive manner but also reveal new insights on how to approach certain classes of problems.
Starting with chapter 8, the subjects become more advanced, covering Ajax, Spring WebFlow, Security and Web Services. Other interesting chapters include GORM, mapping legacy databases with Hibernate and Plugins. The GORM chapter, for example, does an outstanding job explaining potential pitfalls when working with Grails‘ domain layer. The chapter on ‚Integrating Grails‘ explains how configuration and the command line system works which allows you to extend and customize the Grails build system – e.g., building a script to deploy the application directly to Tomcat. Another invaluable chapter introduces the reader to Grails‘ underpinnings, namely the Spring framework. This is by far not a complete introduction to Spring but it gives just enough knowledge to understand what’s going on under the hood and to leverage these internals in own projects or plugins.
Testing support is promoted to be one selling point for Grails but surprisingly, no chapter is dedicated to this topic. This however does not Western union locations mean that testing is not discussed at all. Rather, throughout the construction of the store example, aspects of testing the respective artifacts such as controllers, tag libraries, services etc. are explained. This is certainly a natural way of introducing the topic but makes it somewhat harder to use the book as a reference for Grails‘ testing mechanism.
To summarize, The Definitve Guide to Grails is a good introductory book with the potential to serve as a reference in addition to the official Grails documentation.