(Quick Reference)
                Database Mapping Usage
Domain classes in Grails by default dictate the way they are mapped to the database using sensible defaults. You can customize these with the ORM Mapping DSL. For example create a 
Book domain:
grails create-domain-class Book
And then you can use the 
mapping block to customize the ORM mapping behavior.
class Book {
	String title
	Date releaseDate
	Author author	static mapping = {
		table "books"
		author column:"auth_id"
	}
}Refer to the user guide section on 
ORM Mapping for more information.
Global Database Mapping
You can configure mapping globally in 
grails-app/conf/Config.groovy as follows:
grails.gorm.default.mapping = {
   cache true
   id generator:'sequence'
   'user-type'( type:org.hibernate.type.YesNoType, class:Boolean )
}