grails - 有没有办法在Grails中创建与arbitraray域对象的关系

Question

有没有办法在grails中创建与任意域对象的关联？

就像是

class ThingHolder {
    DomainObject thing;
}

然后

Book b=new Book(title: "Grails 101").save()
Author a=new Author(name: "Abe").save()

ThingHolder t1=new ThingHolder(thing:b).save()
ThingHolder t2=new ThingHolder(thing: a).save()

以便

ThingHolder.get(t1.id).thing  // will be a Book

和

ThingHolder.get(t2.id).thing  // will be an Author.

Answer 1

我仍在寻找一种更轻松的方式来执行此操作，但这似乎可以完成工作。

class ThingHolder {
    static constraints = {
        thing bindable:true // required so 'thing' is bindable in default map constructor.
    }

    def grailsApplication;

    Object thing;

    String thingType;
    String thingId;

    void setThing(Object thing) {    //TODO: change Object to an interface
        this.thing=thing;
        this.thingType=thing.getClass().name
        this.thingId=thing.id;       //TODO: Grailsy way to get the id
    }

    def afterLoad() {
        def clazz=grailsApplication.getDomainClass(thingType).clazz
        thing=clazz.get(thingId);
    }
}

假设您有一个Book和Author(不覆盖域对象的ID属性)。

def thing1=new Author(name : "author").save(failOnError:true);
def thing2=new Book(title: "Some book").save(failOnError:true);

new ThingHolder(thing:thing1).save(failOnError:true)
new ThingHolder(thing:thing2).save(failOnError:true)

ThingHolder.list()*.thing.each { println it.thing }

在这两个答案中，我发现了一些非常有用的技巧。

How to make binding work in default constructor with transient values.

How to generate a domain object by string representation of class name