How to create an index for foreign key in Grails GORM

Question

Suppose you have the following domain classes

class User {
    static hasMany = [books:Book]
}

class Book {
    static belongsTo = [user:User]
}

Gorm adds a user_id column and a foreign key to the Book table. How can I add an index on this column?

Answer 1

It seems the simplest way works as expected. You don't need to specify the foreign key or something else.

class Book {
    static belongsTo = [user:User]
    static mapping = {
        user index:'index_book_user_id'
    }
}