Hibernate"discriminator-value"用法

转自：https://blog.csdn.net/iteye_3357/article/details/81862615

 1 可能经常遇到这样的情况：
 2
 3        在数据库表中会有这样的一个字段用来区别记录的属性，如：在客户表中有一个字段表示客户级别，当这个记录为A时是一级客户，为B时是二级客户。在用hiberante做OR表示时类可能是这样的：
 4
 5        public class Customer{
 6
 7           private String flag;   //表示客户的级别
 8
 9           ...
10
11        }
12
13        然后，在程序中手动控制flag的值，但是这样当每个级的客户有不同的属性时Customer类将包含所有级别的属性，这样不是很好。
14
15        hibernate提供一个Discriminator映射的方法，就是把一个表映射成不同的类，有不同的属性。
16
17        public class Customer{
18
19           //包含所有级别的公共属性
20
21           ...
22
23         }
24
25
26
27        public class CustomerA extends Customer{
28
29        //只包括一级客户的特有属性
30
31         }
32
33        public class CustomerB extends Customer{
34
35        //只包含二级客户特有的属性
36
37         }
38
39 这样更符合面向对象的原则，然后在hbm.xml中这样写：
40
41 <id name="id" type="int">
42
43     ...
44
45 </id>
46
47 <discriminator column="flag" type="string" />
48
49 <!-- 公共属性的映射 -->
50
51 <subclass name="CustomerA" discriminator-value="A">
52
53 <!-- 一级客户特有属性的映射 -->
54
55 </subclass>
56
57 <subclass name="CustomerB" discriminator-value="B">
58
59 <!-- 二级客户特有属性的映射 -->
60
61 </subclass>
62
63 这样就可以单独的用CustomerA,CustomerB这样的实例了，做数据库修改时就不用关心flag字段的值了，会自动的加A或B。
64
65 如果是使用hibernate Annotation而不是xml来描述映谢关系，代码如下：
66
67 @Entity
68
69 @Table(name = "customer")
70
71 @Inheritance(strategy = InheritanceType.SINGLE_TABLE)
72
73 @DiscriminatorColumn(name = "flag", discriminatorType = DiscriminatorType.STRING)
74
75 public class Customer{
76
77 }
78
79 @Entity
80
81 @DiscriminatorValue(value = "A")
82
83 public class CustomerA extends Customer{
84
85 }
86
87 @Entity
88
89 @DiscriminatorValue(value = "B")
90
91 public class CustomerB extends Customer{
92
93 }
94
95 这样就可以了。

2.

 1 public class Singer {
 2     private String region;
 3     private Long id;
 4     private Set<Song> songs = new HashSet<Song>();
 5
 6     public String getRegion() {
 7         return region;
 8     }
 9
10     public void setRegion(String region) {
11         this.region = region;
12     }
13
14     public Long getId() {
15         return id;
16     }
17
18     public void setId(Long id) {
19         this.id = id;
20     }
21
22     public Set<Song> getSongs() {
23         return songs;
24     }
25
26     public void setSongs(Set<Song> songs) {
27         this.songs = songs;
28     }
29
30     public void addSong(Song song){
31         songs.add(song);
32         song.setSinger(this);
33     }
34 }

3.

 1 public class SingleSinger extends Singer {
 2     private String name;
 3     private char sex;
 4
 5     public String getName() {
 6         return name;
 7     }
 8
 9     public void setName(String name) {
10         this.name = name;
11     }
12
13     public char getSex() {
14         return sex;
15     }
16
17     public void setSex(char sex) {
18         this.sex = sex;
19     }
20 }

3.

 1 package edu.jlu.fuliang.domain;
 2
 3 import java.util.HashSet;
 4 import java.util.Set;
 5
 6 public class CompositeSinger extends Singer {
 7     private Set<SingleSinger> singleSingers = new HashSet<SingleSinger>();
 8
 9     public Set<SingleSinger> getSingleSingers() {
10         return singleSingers;
11     }
12
13     public void setSingleSingers(Set<SingleSinger> singleSingers) {
14         this.singleSingers = singleSingers;
15     }
16     public void addSinger(SingleSinger singleSinger){
17         singleSingers.add(singleSinger);
18     }
19 }

5.

 1 public class Band extends CompositeSinger {
 2     private String name;
 3
 4     public String getName() {
 5         return name;
 6     }
 7
 8     public void setName(String name) {
 9         this.name = name;
10     }
11 }

6.

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4
 5 <hibernate-mapping package="edu.jlu.fuliang.domain">
 6     <class name="Singer" table="SINGER">
 7       <id name="id" type="java.lang.Long">
 8          <column name="SINGER_ID"/>
 9          <generator class="identity"/>
10       </id>
11
12      <discriminator column="TYPE" type="string"/>
13
14      <property name="region" type="java.lang.String">
15          <column name="REGION"/>
16      </property>
17
18       <set name="songs" table="SONG" inverse="true" cascade="save-update">
19          <key column="SINGER_ID"/>
20          <one-to-many class="Song"/>
21       </set>
22
23       <subclass name="SingleSinger" discriminator-value="1">
24          <property name="name" type="java.lang.String">
25               <column name="NAME"/>
26          </property>
27          <property name="sex" type="java.lang.Character">
28              <column name="SEX"/>
29          </property>
30       </subclass>
31
32       <subclass name="CompositeSinger" discriminator-value="2">
33          <set name="singleSingers" table="SINGER" cascade="save-update" lazy="false">
34              <key column="COMPSITESINGER_ID"/>
35              <one-to-many class="SingleSinger"/>
36          </set>
37       </subclass>
38
39       <subclass name="Band" discriminator-value="3">
40           <set name="singleSingers" table="SINGER" cascade="save-update">
41              <key column="BAND_ID"/>
42              <one-to-many class="SingleSinger"/>
43          </set>
44       </subclass>
45     </class>
46 </hibernate-mapping>