java - GAE 数据存储区使用 JPA 生成字符串 key

Question

由于不可能仅使用长 ID，因此我尝试使用生成的字符串键。我有三个类 User、Topic、Comments 和 User - 1:n - Topic - 1:n -注释。

类(class)评论:

@Entity
public class Comment implements Serializable{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value = "true")
    private String key;
    @ManyToOne
    private User author;
    @ManyToOne
    private Topic topic;

类(class)用户:

@Entity
public class User implements Serializable{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value = "true")
    private String key;

    @Unique
    private String username;

类主题:

@Entity
public class Topic implements Serializable{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true")
    private String key;
    @ManyToOne(cascade = CascadeType.ALL)
    private User author;
    @OneToMany(cascade = CascadeType.ALL)
    private List<Comment> comments;

现在，当我尝试保存新用户时，出现以下异常

Invalid primary key for User.  Cannot have a null primary key field if the field is unencoded and of type String.  Please provide a value or, if you want the datastore to generate an id on your behalf, change the type of the field to Long. 

是否可以在不手动使用 KeyFactory 的情况下生成字符串 ID？如果是的话我的代码有什么问题吗？

谢谢

Answer 1

IIRC IDENTITY 策略是生成数字(或键)id。 如果您使用 JDO，则可以使用自动生成的 UUID 样式 id。 请参阅https://developers.google.com/appengine/docs/java/datastore/jdo/creatinggettinganddeletingdata#Keys