java - Hibernate/JPA 在合并后获取数据库中具有默认值的列的值

Question

案例:合并对象后，我想获取映射到数据库端具有默认值的列的字段值。

表格:

CREATE TABLE IF NOT EXISTS `db`.`OBJECT` (
  `OBJECT_ID` INT NOT NULL AUTO_INCREMENT,
  `NAME` VARCHAR(64) NULL,
  `CREATED_ON` DATETIME NULL DEFAULT CURRENT_TIMESTAMP,
  `EDITED_ON` DATETIME NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
)

类:

@Entity
@Table(name="OBJECT")
public class SomeObject {
    private int id;
    private String name;
    private Timestamp createdOn;
    private Timestamp editedOn;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "ID")
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @Column(name = "NAME")
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Column(name = "CREATED_ON", insertable = false, updatable = false)
    public Timestamp getCreatedOn() {
        return createdOn;
    }

    public void setCreatedOn(Timestamp createdOn) {
        this.createdOn = createdOn;
    }

    @Column(name = "EDITED_ON", insertable = false, updatable = false)
    public Timestamp getEditedOn() {
        return editedOn;
    }

    public void setEditedOn(Timestamp editedOn) {
        this.editedOn = editedOn;
    }
}

DAO:

@Transactional
public class ObjectDAO {
    @PersistenceContext
    private EntityManager entityManager;

    public someObject merge(someObject someObject) {
        return entityManager.merge(someObject);
    }
}

我想做什么:

SomeObject someObject = new SomeObject();
someObject.setName("name");
SomeObject insertedObject = objectDAO.merge(someObject);
System.out.println(insertedObject.getId());
System.out.println(insertedObject.getEditedOn());

结果:对象被插入到数据库中，所有默认值都正确生成。

问题:为什么第二个 println 打印 null，但第一个 println 打印插入数据库的 Id 的正确值？

Answer 1

在你执行这一行之前:

System.out.println(insertedObject.getEditedOn());

您必须通过调用“刷新”(同步)您的更新:entityManager.flush();