Question

I am using Grails 1.3.6 and I am having problems getting saves to cascade properly. The problem is specifically with classes that have two parent classes. A simplified version of what I am attempting is this:

class Location {
    String city
    static hasMany = [authors: Author, publishers: Publisher]
}

class Author {
    String name
    static belongsTo = [location: Location]
    static hasMany = [books: Book]
}

class Publisher {
    String name
    static belongsTo = [location: Location]
    static hasMany = [books: Book]
}

class Book {
    String title
    static belongsTo = [author: Author, publisher: Publisher]
}

class Srv1Service {

    static transactional = true

    def loadData() {
        def l1 = new Location(city: "London")

        def a1 = new Author(name: "Graham Greene")
        l1.addToAuthors(a1)

        def p1 = new Publisher(name: "Some Press")
        l1.addToPublishers(p1)

        def b1 = new Book(title: "The Comedians")
        a1.addToBooks(b1)
        p1.addToBooks(b1)

        l1.save()
    } 
}

If I run the above loadData, the Book instance is saved before the Publisher instance, resulting in the error “not-null property references a null or transient value: adhoc.Book.publisher”.

I have tried various different ways of defining the relationships with little success. I have tried interim saves, and this does work, but I can see that parent tables are updated as I save the child data – ie Location, Author and Publisher all get updated to version 1. (And also I would like to keep the code as simple as I can.) I would like to avoid linking tables.

Any advice is gratefully received!

Answer 1

Okay, so the key here is that saves are cascaded from parent to children. You have a problem when it comes to Book because Book is the child to both Publisher and Author. GORM tries to save Location, Location tries to save Author, Author tries to save Book BUT the save fails because Book has a transient Publisher.

Try adding an intermediate save right before you create your Book:

def loadData() {
    def l1 = new Location(city: "London")

    def a1 = new Author(name: "Graham Greene")
    l1.addToAuthors(a1)

    def p1 = new Publisher(name: "Some Press")
    l1.addToPublishers(p1)
    l1.save() // add this save

    def b1 = new Book(title: "The Comedians")
    a1.addToBooks(b1)
    p1.addToBooks(b1)

    l1.save()
} 

I created a local Grails project with your domain classes adding in this save. The cascading is working as you would expect.