JPA--联合主键

联合主键的一些知识：

使用@EmbeddedId标示联合主键；

在联合主键类中只是定义确定联合主键的字段即可；
* 联合主键类的规则
* 1.必须包含一个无参的构造函数
* 2.必须实现序列化接口
* 3.必须重写hashCode和equals方法，而且equals方法的参数必须包括确定联合主键的所有字段

 

 

联合主键类的定义：

 1 package com.yl.demo1.bean.JointPK;

 2 

 3 import java.io.Serializable;

 4 

 5 import javax.persistence.Column;

 6 import javax.persistence.Embeddable;

 7 

 8 /**

 9  * 在联合主键类中只是定义确定联合主键的字段即可

10  * 联合主键类的规则

11  *     1.必须包含一个无参的构造函数

12  *     2.必须实现序列化接口

13  *  3.必须重写hashCode和equals方法，而且equals方法的参数必须包括确定联合主键的所有字段

14  * @author yul

15  *

16  *@Embeddable--告诉其它类，在使用AieLinePK时只是使用AieLinePK的属性作为实体的持久化属性

17  */

18 

19 @Embeddable //嵌入

20 public class AirLinePK implements Serializable {

21     private String startCity;//航空中每个城市都有一个三位的字母标识符

22     private String endCity;

23     

24     public AirLinePK(){}

25     

26     

27     public AirLinePK(String startCity, String endCity) {

28         this.startCity = startCity;

29         this.endCity = endCity;

30     }

31     @Column(length=3)

32     public String getStartCity() {

33         return startCity;

34     }

35     public void setStartCity(String startCity) {

36         this.startCity = startCity;

37     }

38     @Column(length=3)

39     public String getEndCity() {

40         return endCity;

41     }

42     public void setEndCity(String endCity) {

43         this.endCity = endCity;

44     }

45     

46     @Override

47     public int hashCode() {

48         final int prime = 31;

49         int result = 1;

50         result = prime * result + ((endCity == null) ? 0 : endCity.hashCode());

51         result = prime * result

52                 + ((startCity == null) ? 0 : startCity.hashCode());

53         return result;

54     }

55     @Override

56     public boolean equals(Object obj) {

57         if (this == obj)

58             return true;

59         if (obj == null)

60             return false;

61         if (getClass() != obj.getClass())

62             return false;

63         AirLinePK other = (AirLinePK) obj;

64         if (endCity == null) {

65             if (other.endCity != null)

66                 return false;

67         } else if (!endCity.equals(other.endCity))

68             return false;

69         if (startCity == null) {

70             if (other.startCity != null)

71                 return false;

72         } else if (!startCity.equals(other.startCity))

73             return false;

74         return true;

75     }

76     

77     

78 }

 

 1 package com.yl.demo1.bean.JointPK;

 2 

 3 import javax.persistence.Column;

 4 import javax.persistence.EmbeddedId;

 5 import javax.persistence.Entity;

 6 

 7 @Entity

 8 public class AirLine {

 9     private AirLinePK id;

10     private String name;

11     

12     

13     

14     public AirLine(){}

15     

16     public AirLine(AirLinePK id) {

17         this.id = id;

18     }

19     

20     public AirLine(String startCity, String endCity, String name) {

21         this.id = new AirLinePK(startCity, endCity);

22         this.name = name;

23     }

24     

25     @EmbeddedId 

26     public AirLinePK getId() {

27         return id;

28     }

29     public void setId(AirLinePK id) {

30         this.id = id;

31     }

32     @Column(length=20)

33     public String getName() {

34         return name;

35     }

36     public void setName(String name) {

37         this.name = name;

38     }

39 

40 }

 

常用操作:

 1 @Test

 2     public void save() {

 3         EntityManagerFactory factory = Persistence.createEntityManagerFactory("YL");

 4         EntityManager em = factory.createEntityManager();

 5         em.getTransaction().begin();//事务开始

 6         

 7         em.persist(new AirLine("PEK", "SHA", "北京飞上海"));

 8         

 9         em.getTransaction().commit();

10         em.close();

11         factory.close();

12     }