继承映射

以Person，Student，Teacher三者的实现为例，关系如下图(Student和Teacher是Person类的子类)：

三种策略：

　　第一种(SINGLE_TABLE)：将所有类的字段都放在一个表之中,一张总表。

Person:

 1 package com.bjsxt.hibernate;
 2 
 3 import javax.persistence.DiscriminatorColumn;
 4 import javax.persistence.DiscriminatorType;
 5 import javax.persistence.DiscriminatorValue;
 6 import javax.persistence.Entity;
 7 import javax.persistence.GeneratedValue;
 8 import javax.persistence.Id;
 9 import javax.persistence.Inheritance;
10 import javax.persistence.InheritanceType;
11 
12 @Entity
13 @Inheritance(strategy=InheritanceType.SINGLE_TABLE)
14 @DiscriminatorColumn(name="discriminator",discriminatorType=DiscriminatorType.STRING)
15 @DiscriminatorValue("person")
16 public class Person {
17     
18     private Integer id;
19     
20     private String name;
21 
22     @Id
23     @GeneratedValue
24     public Integer getId() {
25         return id;
26     }
27 
28     public void setId(Integer id) {
29         this.id = id;
30     }
31 
32     public String getName() {
33         return name;
34     }
35 
36     public void setName(String name) {
37         this.name = name;
38     }
39 }
View Code

Student:

 1 package com.bjsxt.hibernate;
 2 
 3 import javax.persistence.DiscriminatorValue;
 4 import javax.persistence.Entity;
 5 
 6 @Entity
 7 @DiscriminatorValue("student")
 8 public class Student extends Person {
 9     
10     private Integer score;
11 
12     public Integer getScore() {
13         return score;
14     }
15 
16     public void setScore(Integer score) {
17         this.score = score;
18     }
19     
20 }
View Code

Teacher:

 1 package com.bjsxt.hibernate;
 2 
 3 import javax.persistence.DiscriminatorValue;
 4 import javax.persistence.Entity;
 5 
 6 @Entity
 7 @DiscriminatorValue("teacher")
 8 public class Teacher extends Person {
 9     private String title;
10 
11     public String getTitle() {
12         return title;
13     }
14 
15     public void setTitle(String title) {
16         this.title = title;
17     }
18 }
View Code

jar包链接: https://pan.baidu.com/s/1gfh37wf 密码: rj2k

代码链接: https://pan.baidu.com/s/1c2062ek 密码: ix9t

　　第二种(TABLE_PER_CLASS)：每个表都是完整的信息，主键都取自一个中间表，以保持三个表主键的一致性,每个类分别一张表。

Person:

 1 package com.bjsxt.hibernate;
 2 
 3 import javax.persistence.Entity;
 4 import javax.persistence.GeneratedValue;
 5 import javax.persistence.GenerationType;
 6 import javax.persistence.Id;
 7 import javax.persistence.Inheritance;
 8 import javax.persistence.InheritanceType;
 9 import javax.persistence.TableGenerator;
10 
11 @Entity
12 @Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
13 @TableGenerator(
14         name="t_gen",
15         table="t_gen_table",
16         pkColumnName="t_pk",//key的字段名
17         valueColumnName="t_value",//value的字段名
18         pkColumnValue="person_pk",//字段值
19         initialValue=1,
20         allocationSize=1
21         )
22 public class Person {
23     
24     private Integer id;
25     
26     private String name;
27 
28     @Id
29     @GeneratedValue(generator="t_gen",strategy=GenerationType.TABLE)
30     public Integer getId() {
31         return id;
32     }
33 
34     public void setId(Integer id) {
35         this.id = id;
36     }
37 
38     public String getName() {
39         return name;
40     }
41 
42     public void setName(String name) {
43         this.name = name;
44     }
45 }
View Code

Student:

 1 package com.bjsxt.hibernate;
 2 
 3 import javax.persistence.Entity;
 4 
 5 @Entity
 6 public class Student extends Person {
 7     
 8     private Integer score;
 9 
10     public Integer getScore() {
11         return score;
12     }
13 
14     public void setScore(Integer score) {
15         this.score = score;
16     }
17     
18 }
View Code

Teacher:

 1 package com.bjsxt.hibernate;
 2 
 3 import javax.persistence.Entity;
 4 
 5 @Entity
 6 public class Teacher extends Person {
 7     private String title;
 8 
 9     public String getTitle() {
10         return title;
11     }
12 
13     public void setTitle(String title) {
14         this.title = title;
15     }
16 }
View Code

jar包链接: https://pan.baidu.com/s/1gfh37wf 密码: rj2k

代码链接: https://pan.baidu.com/s/1bprLc9x 密码: 3dgi

　　第三种(JOINED)：子类对应的表和父类对应的表建立主键关联，每个子类一张表，父类对应的表保存公共属性字段，子类对应的表保存子类特有的对应字段。

Person:

 1 package com.bjsxt.hibernate;
 2 
 3 import javax.persistence.Entity;
 4 import javax.persistence.GeneratedValue;
 5 import javax.persistence.Id;
 6 import javax.persistence.Inheritance;
 7 import javax.persistence.InheritanceType;
 8 
 9 @Entity
10 @Inheritance(strategy=InheritanceType.JOINED)
11 public class Person {
12     
13     private Integer id;
14     
15     private String name;
16 
17     @Id
18     @GeneratedValue()
19     public Integer getId() {
20         return id;
21     }
22 
23     public void setId(Integer id) {
24         this.id = id;
25     }
26 
27     public String getName() {
28         return name;
29     }
30 
31     public void setName(String name) {
32         this.name = name;
33     }
34 }
View Code

Student:

 1 package com.bjsxt.hibernate;
 2 
 3 import javax.persistence.Entity;
 4 
 5 @Entity
 6 public class Student extends Person {
 7     
 8     private Integer score;
 9 
10     public Integer getScore() {
11         return score;
12     }
13 
14     public void setScore(Integer score) {
15         this.score = score;
16     }
17     
18 }
View Code

Teacher:

 1 package com.bjsxt.hibernate;
 2 
 3 import javax.persistence.Entity;
 4 
 5 @Entity
 6 public class Teacher extends Person {
 7     private String title;
 8 
 9     public String getTitle() {
10         return title;
11     }
12 
13     public void setTitle(String title) {
14         this.title = title;
15     }
16 }
View Code

jar包链接: https://pan.baidu.com/s/1gfh37wf 密码: rj2k

代码链接: https://pan.baidu.com/s/1c12sjIw 密码: 1dzr

posted @ 2017-04-24 17:26  流年如水烟雨随风  阅读(584)  评论(0)  编辑  收藏  举报