In part 4, we'll introduce you to some of the most advanced features that Grails has to offer. You'll learn about performance tuning, legacy integration, database transactions, custom build processes, and even how to develop and publish your own plugins. Chapter 13 will take you on into GORM-the Grails object relational mapping implementation. You'll learn a lot about less-frequently used modeling options that can be real time-savers. You'll also explore caching, performance profiling, and some comprehensive legacy-integration examples. Chapter 14 takes you into the heart of Spring integration in Grails. You'll learn all the different ways of defining and interacting with Spring-managed beans in your application. We'll then tour transactions-how they work and what they're useful for.