java 休眠注释-使用@MappedSuperclass 继承-值未设置为基类字段-奇怪的错误

hibernate annotation- inheritance with @MappedSuperclass - values are not being set to base class fields- strange error

提问by gtiwari333

I was following Hibernate: Use a Base Class to Map Common Fieldsand openjpa inheritance tutorialto put common columns like ID, lastModifiedDate etc in base table.

我正在关注 Hibernate：使用基类映射公共字段和 openjpa 继承教程将公共列（如 ID、lastModifiedDate 等）放在基表中。

My annotated mappings are as follow :

我的注释映射如下：

BaseTable :

基表：

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

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

Person table -

人表——

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

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

Create statement generated :

创建语句生成：

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

After I save a Person object to db,

在我将 Person 对象保存到数据库后，

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

getSession().save(p);

I am setting the date field but, it is saving the record with generated ID and LastModifiedDate = null, and Name="Test".

我正在设置日期字段，但它使用生成的 ID 和 LastModifiedDate = null 以及 Name="Test" 保存记录。

Insert Statement :

插入语句：

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

Read by ID query :When I do hibernate query (get By ID) as below, It reads person by given ID.

按 ID 查询读取：当我按如下方式进行休眠查询（按 ID 获取）时，它会按给定的 ID 读取人员。

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 :

ReadAll 查询：

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

Corresponding SQL for read all

读取全部对应的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_ ]

But when I print out the list in console, its being more weird. it is selecting List of Person object with

但是当我在控制台中打印出列表时，它变得更奇怪了。它正在选择人员对象列表

• ID fields = all 0 (why all 0 ?)
• LastModifiedDate = null
• Name fields have valid values

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

I don't know whats wrong here. Could you please look at it?

我不知道这里出了什么问题。你能看一下吗？

FYI,

供参考，

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

我的 Hibernate 核心版本：4.1.2，MySQL 连接器版本：5.1.9。

In summary, There are two issues here

总结一下，这里有两个问题

• Why I am getting All ID Fields =0 when using read all?
• Why the LastModifiedDate is not being inserted?

• 为什么我在使用 read all 时得到 All ID Fields =0？
• 为什么未插入 LastModifiedDate？

回答by Ilya

Use

利用

@Temporal(TemporalType.DATE)  

annotation on Date

注释在 Date

For ID generation use strategy.

对于 ID 生成使用策略。

@GeneratedValue(strategy=GenerationType.AUTO) 

or

或者

@GeneratedValue(strategy=GenerationType.IDENTITY) 

or using sequance

或使用序列

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

also you can make property access in your child class:

您也可以在子类中访问属性：

public abstract class BaseTable {

    protected int id;

    protected Date lastModifiedDate;  
// ...  
}    

and

和

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

@Id
@GeneratedValue
@Column(name = "id")
public getId()
{
   return super.id;
}

setId(log id)
{
   super.id = id;
}

@Column(name = "lastmodifieddate")
@Temporal(TemporalType.DATE) 
public getLastModifiedDate()
{
   return super.lastModifiedDate;
}

setLastModifiedDate(Date date)
{
   super.lastModifiedDate = date;
}

public getName()
// ...
}

回答by Rehman

Try this out in BaseTable class

在 BaseTable 类中试试这个

@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;
}

where BaseTable class should have @MappedSuperclass. And there must be one generated date field in an entity.

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;
    }



}