google-app-engine - 持久对象列表

Question

我懂了
“javax.jdo.JDOFatalUserException:don.Comment.id的元数据中发生错误:无法具有java.lang.String主键，并且不能成为子对象(拥有字段是don.Post.comments)。
NestedThrowables:“

运行grails + app-engine webapp时

我怎样才能解决这个问题？

class Comment.groovy

import javax.jdo.annotations.*;

@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable="true")
class Comment implements Serializable {

@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
String id

@Persistent(mappedBy="comments")
Post post

@Persistent
String name

@Persistent
String email

@Persistent
String url

static constraints = {
    id( visible:false)
}
}

class Post.groovy
    @PersistenceCapable(identityType = IdentityType.APPLICATION, detachable="true")
    class Post implements Serializable {

@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
Long id

@Persistent
String title

@Persistent 
String content

//static hasMany = [comments:Comment]

@Persistent(defaultFetchGroup = "true")
Comment comments

static constraints = {
    id( visible:false)
}
}

Answer 1

对于子类，主键必须是com.google.appengine.api.datastore.Key值(或编码为字符串)，请参见http://code.google.com/appengine/docs/java/datastore/creatinggettinganddeletingdata.html#Keys