(Quick Reference)
                cascade
Purpose
Configures the cascading behavior of an association.
Examples
class Author {    static hasMany = [books: Book]    static mapping = {
        books cascade: 'all-delete-orphan'
    }
}Description
Usage: 
association_name(cascade:string)Arguments:
- cascade- The cascading behavior to define. Can be one or more (comma-separated) of- all,- merge,- save-update,- delete,- lock,- refresh,- evict,- replicateor- all-delete-orphan(one-to-many associations only).
By default GORM configures a cascading policy of "all" in the case where one entity "belongs to" another. For example:
class Book {
    static belongsTo = [author: Author]
}class Author {
    static hasMany = [books: Book]
}Here all persistence operations will cascade from the 
Author domain to the 
Book domain. So when an 
Author is deleted so will all the associated books.
If the association doesn't define an owner (a "belongs to" relationship):
class Author {
    static hasMany = [books: Book]
}then GORM uses a cascading policy of "save-update" by default. So if an 
Author is deleted the 
Book associated domains won't be deleted. Use the 
cascade argument on an association to customize this behavior:
class Author {    static hasMany = [books: Book]    static mapping = {
        books cascade: 'all-delete-orphan'
    }
}Using this configuration a 
Book will also be deleted if it is removed (orphaned) from an 
Author's 
books association.
See the section on 
transitive persistence in the Hibernate user guide.