Grails: multiple relationships between two domain objects

Question

I am trying to implement two different types of relationships between two domain classes in Grails.

Consider the following; I have two domain classes, an Author and Book class with an Author having many Books.

class Author{           
   String name 
}

class Book{
   String title
   static belongsTo = [author:Author]

}

The above depicts a very basic one to many relationship between an Author and a Book. But I also want an Author to have a concept of a list of favourite books. This would ideally be represented as a separate one to many relationship describing the same Book object as a list and persisted as such.

class Author{          
   String name
   static hasMany = [favouriteBooks: Book]

   static mapping = {
        favouriteBooks joinTable: [name: 'favourite_books',
                key: 'author_id']
   }
}

class Book{
   String title
   static belongsTo = [client:Client]

}

I have tried to describe this as above (among many other methods) and ultimately the database table (favourite_books) is not created. I do not get any errors. This is the only way I can think of doing this without using any extra objects which I would like to avoid to keep the model simple. I feel I'm on the right track but maybe missing some vital piece of the puzzle.

Any help would be much appreciated.

Answer 1

Finally figured this out. Thanks to Don for pointing me in the direction of the db-reverse-engineer plugin which helped expose the key property that allows for this mapping strategy. Basically it all came down to using GORM's mappedBy association setting to explicitly tell Grails how the multiple hasMany references should be mapped. The class files that worked are as follows:

class Author {

    String name
    static hasMany = [books: Book, favourites: Book]

    // need to disambiguate the multiple hasMany references with the 
    // 'mappedBy' property:
    static mappedBy =   [books: "author",
                        favourites: "authors"]
}

class Book {

    String title
    Author author

    static hasMany = [authors: Author]
    static belongsTo = [Author]
}

Thanks again for the help