>我有一个MySQL表:
mysql> show create table itemsG
*************************** 1. row ***************************
Table: items
Create Table: CREATE TABLE `items` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(128) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`created` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
1 row in set (0.02 sec)
我通过实体类从 Java 程序创建新行:
@Entity
@Table(name = "items", schema = "office_db")
@XmlRootElement
@NamedQueries({
@NamedQuery(name = "Items.findAll", query = "SELECT i FROM Items i"),
@NamedQuery(name = "Items.findById", query = "SELECT i FROM Items i WHERE i.id = :id"),
@NamedQuery(name = "Items.findByName", query = "SELECT i FROM Items i WHERE i.name = :name"),
@NamedQuery(name = "Items.findByCreated", query = "SELECT i FROM Items i WHERE i.created = :created")
})
public class Items implements Serializable {
@Column(name = "name",length = 128)
private String name;
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "id")
private Integer id;
@Basic(optional = false)
@Column(name = "created")
@Temporal(TemporalType.TIMESTAMP)
private Date created;
@OneToMany(mappedBy = "itemId")
private Collection<Documents> documentsCollection;
@OneToMany(cascade = CascadeType.ALL, mappedBy = "items")
private Collection<ItemAttributes> itemAttributesCollection;
(more stuff ...)
我只设置了 NAME 列,正如预期的那样,默认情况下设置了 ID 和 CREATED:
mysql> select * from items;
+----+--------+---------------------+
| id | name | created |
+----+--------+---------------------+
| 2 | Case 2 | 2017-10-31 13:47:52 |
| 3 | Case 3 | 2017-10-31 13:48:02 |
+----+--------+---------------------+
2 rows in set (0.00 sec)
但是,当我稍后在同一会话中将表重新加载到 Java 中时:
public List<Items>findItems(){
TypedQuery<Items> query=
em.createNamedQuery("Items.findAll",Items.class);
return query.getResultList();
}
ID 列已正确加载,但 CREATED(已创建)列显示为空白。如果我重新启动应用程序(这在玻璃鱼服务器上运行),CREATED会正确显示。我的猜测是,造成这种差异的原因是 ID 上的@GeneratedValue注释,但我似乎无法将其应用于 CREATED,或者至少不能天真地将其应用于 CREATED。加载生成的时间戳的正确方法是什么?
我的难题的答案似乎是调用em.refresh()
,根据这个: 使 JPA EntityManager 会话无效 - 这是针对 Hibernate 的,但对于 EclipseLink 来说似乎是一样的。就我而言,我遇到了一个例外,但我会在另一个问题中发布。