Java 如何在 JPA - GAE/J 中使属性可以为空？
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How to make a property nullable in JPA - GAE/J?
提问by Tahir Akram
I have a entity class User. I want to add some more properties but to keep them nullable.
我有一个实体类User。我想添加更多属性，但要保持它们可为空。
What is the annotation used for this in JPA?
JPA 中用于此的注释是什么？
I am using JPA in Google App Engine.
我在 Google App Engine 中使用 JPA。
采纳答案by Henning
Properties are nullable by default in JPA, except primitive types. You can control nullability using the nullableproperty of the @Column annotation, like so:
默认情况下，JPA 中的属性可为空，原始类型除外。您可以使用nullable@Column 注释的属性控制可空性，如下所示：
//not nullable
@Column(nullable = false)
private String prop1;
//nullable
@Column(nullable = true)
private String prop2;
//default = nullable
@Column
private String prop3;
回答by coldiron
In your Entity class use Integer, Double, rather than int and double.
在您的实体类中使用 Integer、Double，而不是 int 和 double。
@Entity
public class AnyTable {
...
public double myValue; // !! dont use in this way - this can never be null!
public Double myValue; // BETTER !
