SpringData JPA复合主键

最新推荐文章于 2020-03-18 00:21:29 发布

一块巧克力@

最新推荐文章于 2020-03-18 00:21:29 发布

阅读量205

点赞数

分类专栏： Springboot相关知识异常处理文章标签：异常处理

Springboot相关知识同时被 2 个专栏收录

9 篇文章

订阅专栏

异常处理

4 篇文章

订阅专栏

上一篇博客简单介绍了SpringData JPA实现简单的CRUD，分页与多条件的排序，那里的主键类型是Long,有时我们会遇到主键不是一个的，复合主键，经过调研如下。确定一个人，不能只根据他的姓名来确定，因为会有重名，现在我们假设姓名、身份证号确定唯一一个人。

复合主键：一张表存在多个字段共同组成一个主键，这多个字段的组合不能重复，但是单独一个可以重复。

例子：姓名和省份证号共同组成了主键

二、采用@IdClass来注解复合主键

过程和@Embeddable差不多，这里直接贴例子。

@Entity

@Table(name = "people")

@IdClass(PeopleKey.class)

public class People implements Serializable {

// @EmbeddedId

// private PeopleKey id;

@Id

@Column(name = "name")

private String name;

@Id

@Column(name = "idcardno")

private String idcardno;

@Column(name = "age")

private int age;

@Column(name = "address")

private String address;

}

public class PeopleKey implements Serializable {

// @Id

// @Column(name = "name")

private String name;

// @Id

// @Column(name = "idcardno")

private String idcardno;

}

采用这个方法的我参考博客里有一篇，写的比较详细，但是感觉这个方法不好，本身就已经在PeopleKey中把主键给封装了，但是在实体类People中还要把复合主键给加入进去，不够简介，采用第一种方法，就很简单，而且也体现了Java类封装的思想。

一、Spring Data Jpa 复合主键

1.1、编写一个复合主键类：PeopleKey　

@Embeddable

public class PeopleKey implements Serializable {

@Column(name = "name")

private String name;

@Column(name = "idcardno")

private String idcardno;

// 省略setter,getter方法

@Override

public String toString() {

return "PeopleKey [name=" + name + ", idcardno=" + idcardno + "]";

}

　　注意：　　

　　1) 实现Serializable接口(否则会报错，错误会直接显示);

　　2)在复合主键的类上，使用注解@Embeddable

　　3) 有默认的public无参数的构造方法（在我这个实例中，我没有添加有参构造方法，所以采用默认的构造方法）

　　如果你在实体类里有有参构造方法，那么一定要有一个无参构造方法，否则运行的时候会报错

1	`org.hibernate.InstantiationException: No` `default` `constructor` `for` `entity: : com.my.model.People`

这个就是没有默认的构造方法造成的，所以要在实体类中加入默认的无参构造方法。

　　4) 重写equals和hashCode方法。equals方法用于判断两个对象是否相同，EntityManger通过find方法来查找Entity时，是根据equals的返回值来判断的。hashCode方法返回当前对象的哈希码（我验证EntityManger，不重写也没事。）；

1.2、编写实体类：People

package com.my.model;

import javax.persistence.*;

@Entity

@Table(name = "people")

//@IdClass(PeopleKey.class)

public class People extends PeopleKey{

　　　　// 复合主键要用这个注解

@EmbeddedId

private PeopleKey id;

@Column(name = "age")

private int age;

@Column(name = "address")

private String address;

// 省略setter,getter方法

@Override

public String toString() {

return "People [id=" + id + ", age=" + age + ", address=" + address

+ "]";

}

1.3 测试：

@Service

public class PeopleService {

@Resource

private PeopleRepository peopleRepository;

public People findOne() {

PeopleKey peopleKey = new PeopleKey();

peopleKey.setName("张三");

peopleKey.setIdcardno("340123");

People people = peopleRepository.findOne(peopleKey);

return people;

}

控制台上的输出结果：

1	`People [id=PeopleKey [name=张三, idcardno=340123], age=3, address=分解分]`

三、EntityManager的验证，直接上代码

package com.my.model;

import java.io.Serializable;

import javax.persistence.Column;

import javax.persistence.Embeddable;

import javax.persistence.Entity;

import javax.persistence.Id;

//@Embeddable

public class PeopleKey implements Serializable {

// @Id

// @Column(name = "name")

private String name;

// @Id

// @Column(name = "idcardno")

private String idcardno;

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getIdcardno() {

return idcardno;

}

public void setIdcardno(String idcardno) {

this.idcardno = idcardno;

}

@Override

public String toString() {

return "PeopleKey [name=" + name + ", idcardno=" + idcardno + "]";

}

package com.my.model;

import java.io.Serializable;

import javax.persistence.*;

@Entity

@Table(name = "people")

@IdClass(PeopleKey.class)

public class People {

// @EmbeddedId

// private PeopleKey id;

@Column(name = "age")

private int age;

@Column(name = "address")

private String address;

// public PeopleKey getId() {

// return id;

// }

//

// public void setId(PeopleKey id) {

// this.id = id;

// }

//

@Id

@Column(name = "name")

private String name;

@Id

@Column(name = "idcardno")

private String idcardno;

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getIdcardno() {

return idcardno;

}

public void setIdcardno(String idcardno) {

this.idcardno = idcardno;

}

public int getAge() {

return age;

}

public People() {

super();

}

public void setAge(int age) {

this.age = age;

}

public String getAddress() {

return address;

}

public void setAddress(String address) {

this.address = address;

}

@Override

public String toString() {

return "People [age=" + age + ", address=" + address + ", name=" + name

+ ", idcardno=" + idcardno + "]";

}

}<br><br>

测试：

@RequestMapping(value = "/useEntityManager")

public void findUseEntityManager() throws Exception

{

PeopleKey peopleKey = new PeopleKey();

peopleKey.setName("张三");

peopleKey.setIdcardno("340123");

People people = entityManager.find(People.class,peopleKey);

System.out.println(people.toString());

}　

结果：

1	`People [age=3, address=分解分, name=张三, idcardno=340123]`

参考网址：

1、https://www.cnblogs.com/linjiqin/archive/2011/03/09/1978680.html

2、http://blog.youkuaiyun.com/qq_35056292/article/details/77892012　

3. https://www.cnblogs.com/boywwj/p/8031106.html