Java 如何在 Hibernate 中使用 UUID 作为字段？
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How to use UUIDs with Hibernate as a field?
提问by Florian Mozart
I'm trying to use generated UUIDs without @Id annotation, because my primary key is something else. The application does not generate an UUID, do you have an idea?
我正在尝试使用没有 @Id 注释的生成的 UUID，因为我的主键是别的东西。应用程序没有生成UUID，你有什么想法吗？
This is my declaration:
这是我的声明：
@Column(name = "APP_UUID", unique = true)
@GeneratedValue(generator="system-uuid")
@GenericGenerator(name="system-uuid", strategy = "uuid")
private String uuid;
I'm using Hibernate 4.3.0 with Oracle10g.
我在 Oracle10g 中使用 Hibernate 4.3.0。
采纳答案by Engineer
回答by user3173787
It's not because your UUID is a primary key that it's mandatory to have it annoted with @GeneratedValue.
并不是因为您的 UUID 是主键，所以必须用@GeneratedValue.
For example, you can do something like this :
例如，您可以执行以下操作：
public class MyClass
{
@Id
private String uuid;
public MyClass() {}
public MyClass (String uuid) {
this.uuid = uuid;
}
}
And in your app, generate a UUID before saving your entity :
在您的应用程序中，在保存您的实体之前生成一个 UUID：
String uuid = UUID.randomUUID().toString();
em.persist(new MyClass(uuid)); // em : entity manager
回答by Tobias Liefke
Check the Javadoc of GeneratedValue:
检查 Javadoc GeneratedValue：
Provides for the specification of generation strategies for the values of primary keys.
提供主键值的生成策略规范。
With other words - it is not possible with just an annotation to initialize a 'none ID' attribute.
换句话说 - 仅使用注释来初始化“无 ID”属性是不可能的。
But you can use @PrePersist:
但你可以使用@PrePersist：
@PrePersist
public void initializeUUID() {
if (uuid == null) {
uuid = UUID.randomUUID().toString();
}
}
