在 Grails 域对象中维护自引用多对多关系的双方

Question

我在获取 grails 中的多对多关系时遇到了一些问题。以下是否有明显错误：

class Person {
    static hasMany = [friends: Person]
    static mappedBy = [friends: 'friends']

    String name
    List friends = []

    String toString() {
        return this.name
    }
}

class BootStrap {
     def init = { servletContext ->
        Person bob = new Person(name: 'bob').save()
        Person jaq = new Person(name: 'jaq').save()
        jaq.friends << bob

        println "Bob's friends: ${bob.friends}"
        println "Jaq's friends: ${jaq.friends}"
     }
} 

我希望 Bob 与 Jaq 成为朋友，反之亦然，但我在启动时得到以下输出：

Running Grails application..
Bob's friends: []
Jaq's friends: [Bob]

（我使用的是 Grails 1.2.0）

Answer 1

这似乎有效：

class Person {
    static hasMany   = [ friends: Person ]
    static mappedBy  = [ friends: 'friends' ]
    String name

    String toString() {
        name
    }
}

然后在 BootStrap 中：

class BootStrap {
     def init = { servletContext ->
        Person bob = new Person(name: 'bob').save()
        Person jaq = new Person(name: 'jaq').save()

        jaq.addToFriends( bob )

        println "Bob's friends: ${bob.friends}"
        println "Jaq's friends: ${jaq.friends}"
     }
} 

我得到以下信息：

Running Grails application..
Bob's friends: [jaq]
Jaq's friends: [bob]