Question

我正在关注Hibernate: Use a Base Class to Map Common Fields和openjpa inheritance tutorial，以便在基表中放置ID，lastModifiedDate等常用列。

我的注释映射如下：

BaseTable：

@MappedSuperclass
public abstract class BaseTable {
    @Id
    @GeneratedValue
    @Column(name = "id")
    private int id;

    @Column(name = "lastmodifieddate")
    private Date lastModifiedDate;
...

人员表 -

    @Entity
    @Table(name = "Person ")
    public class Person extends BaseTable  implements Serializable{

    @Column(name = "name")
    private String name;
...

创建生成的语句：

create table Person (id integer not null auto_increment,  lastmodifieddate datetime, name varchar(255), primary key (id)) ;

将Person对象保存到db后，

Person p = new Person();
p.setName("Test");
p.setLastModifiedDate(new Date());
..

getSession().save(p);

我正在设置日期字段但是，它正在保存带有生成ID和LastModifiedDate = null的记录，而Name =＆＃34; Test＆＃34;。

插入声明：

insert into Person (lastmodifieddate, name) values (?, ?)
binding parameter [1] as [TIMESTAMP] - <null>
binding parameter [2] as [VARCHAR] - Test

通过ID查询读取： 当我按照下面的方式执行休眠查询（get By ID）时，它按给定的ID读取人。

Criteria c = getSession().createCriteria(Person.class);
c.add(Restrictions.eq("id", id));
Person person= c.list().get(0);
//person has generated ID, LastModifiedDate is null

select query select person0_.id as id8_,  person0_.lastmodifieddate as lastmodi8_, person0_.name as name8_ from Person person0_
 - Found [1] as column [id8_]
 - Found [null] as column [lastmodi8_]
 - Found [Test] as column [name8_ ]

ReadAll query：

Query query = getSession().createQuery("from " + Person.class.getName());
List<Person> allPersons=query.list();

读取所有的对应SQL

select query select person0_.id as id8_,  person0_.lastmodifieddate as lastmodi8_, person0_.name as name8_ from Person person0_
- Found [1] as column [id8_]
- Found [null] as column [lastmodi8_]
- Found [Test] as column [name8_ ]
- Found [2] as column [id8_]
- Found [null] as column [lastmodi8_]
- Found [Test2] as column [name8_ ]

但是当我在控制台中打印出列表时，它更加奇怪。它正在选择人物对象列表

ID字段=全0（为什么全0？）
LastModifiedDate = null
名称字段具有有效值

我不知道这里有什么不对。你能看一下吗？

FYI，

My Hibernate-core version：4.1.2，MySQL Connector version：5.1.9。

总之，这里有两个问题

为什么我在使用全部读取时获取所有ID字段= 0？
为什么没有插入LastModifiedDate？

Answer 1

使用

@Temporal(TemporalType.DATE)

<{1}}

上的

注释

用于ID生成使用策略。

Date

或

@GeneratedValue(strategy=GenerationType.AUTO)

或使用sequance

@GeneratedValue(strategy=GenerationType.IDENTITY)

您也可以在您的子类中进行属性访问：

@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "custom_generator")
@SequenceGenerator(name = "custom_generator", sequenceName = "sequance_table")

和

public abstract class BaseTable {

    protected int id;

    protected Date lastModifiedDate;  
// ...  
}

Answer 2

在BaseTable类中尝试这个

@Temporal(value = TemporalType.TIMESTAMP)
@Column(name = "lastmodifieddate", nullable = false,
        columnDefinition = "Timestamp default CURRENT_TIMESTAMP")
@org.hibernate.annotations.Generated(value = GenerationTime.ALWAYS)
public Date getLastModifiedDate( )
{
  return this.lastModifiedDate;
}

其中BaseTable类应该有@MappedSuperclass。并且实体中必须有一个生成的日期字段。

@MappedSuperclass
public abstract class BaseTable {

    protected int id;

    protected Date lastModifiedDate;  


    @Id
    @GeneratedValue(strategy = GenerationType.AUTO) // For Mysql
    // For Oracle or MSSQL @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", unique = true, nullable = false)
    public int getId()
    {
      return this.id;
    }


    @Temporal(value = TemporalType.TIMESTAMP)
    @Column(name = "lastmodifieddate", nullable = false,
            columnDefinition = "Timestamp default CURRENT_TIMESTAMP")
    @org.hibernate.annotations.Generated(value = GenerationTime.ALWAYS)
    public Date getLastModifiedDate( )
    {
      return this.lastModifiedDate;
    }



}

使用@MappedSuperclass进行hibernate注释继承 - 不将值设置为基类字段 - 奇怪的错误

2 个答案: