EJB3 supports the three types of inheritance:

EJB3支持三種類型的繼承:

  • 1.Table per Class Strategy: the <union-class> element in Hibernate

    每個類分別一張表

  • 2.Single Table per Class Hierarchy Strategy: the <subclass> element in Hibernate

    一張總表，即將所有類屬性放入一張表

  • 3.Joined Subclass Strategy: the <joined-subclass> element in Hibernate

    每個子類一張表
下面是實例：Student類(id,name,score)、Teacher類(id,name,title)分別繼承自Person類(id,name)

1、Table Per Class
Person.java
 1package com.bebig.hibernate.model;
 2
 3import javax.persistence.Entity;
 4import javax.persistence.GeneratedValue;
 5import javax.persistence.GenerationType;
 6import javax.persistence.Id;
 7import javax.persistence.Inheritance;
 8import javax.persistence.InheritanceType;
 9import javax.persistence.TableGenerator;
10
11@Entity
12@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
13//用表來管理ID
14@TableGenerator(name = "t_gen", table = "t_gen_table", pkColumnName = "pk_key", valueColumnName = "pk_value", pkColumnValue = "person_pk", initialValue = 1, allocationSize = 1)
15public class Person {
16    private int id;
17
18    private String name;
19
20    @Id
21    @GeneratedValue(generator = "t_gen", strategy = GenerationType.TABLE)
22    public int getId() {
23        return id;
24    }
25
26    public String getName() {
27        return name;
28    }
29
30    public void setId(int id) {
31        this.id = id;
32    }
33
34    public void setName(String name) {
35        this.name = name;
36    }
37
38}
39
Student.java
 1package com.bebig.hibernate.model;
 2
 3import javax.persistence.DiscriminatorValue;
 4import javax.persistence.Entity;
 5
 6@Entity
 7//如果記錄為Student，則標識為student
 8@DiscriminatorValue("student")
 9public class Student extends Person {
10    private int score;
11
12    public void setScore(int score) {
13        this.score = score;
14    }
15
16    public int getScore() {
17        return score;
18    }
19}
20
Teacher.java
 1package com.bebig.hibernate.model;
 2
 3import javax.persistence.DiscriminatorValue;
 4import javax.persistence.Entity;
 5
 6@Entity
 7//如果記錄為Teacher，則標識為teacher
 8@DiscriminatorValue("teacher")
 9public class Teacher extends Person {
10    private String title;
11
12    public void setTitle(String title) {
13        this.title = title;
14    }
15
16    public String getTitle() {
17        return title;
18    }
19
20}
21
hibernate.cfg.xml
1        <mapping class="com.bebig.hibernate.model.Person" />
2        <mapping class="com.bebig.hibernate.model.Teacher" />
3        <mapping class="com.bebig.hibernate.model.Student" />

2、Single Table
Person.java
 1package com.bebig.hibernate.model;
 2
 3import javax.persistence.DiscriminatorColumn;
 4import javax.persistence.DiscriminatorType;
 5import javax.persistence.DiscriminatorValue;
 6import javax.persistence.Entity;
 7import javax.persistence.GeneratedValue;
 8import javax.persistence.Id;
 9import javax.persistence.Inheritance;
10import javax.persistence.InheritanceType;
11
12@Entity
13@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
14//加了一個區別字段來標識每條記錄是哪一種類型
15@DiscriminatorColumn(name = "discriminator", discriminatorType = DiscriminatorType.STRING)
16@DiscriminatorValue("person")
17public class Person {
18    private int id;
19
20    private String name;
21
22    @Id
23    @GeneratedValue
24    public int getId() {
25        return id;
26    }
27
28    public String getName() {
29        return name;
30    }
31
32    public void setId(int id) {
33        this.id = id;
34    }
35
36    public void setName(String name) {
37        this.name = name;
38    }
39
40}
41
其它三個文件同上。
3、Joined
Person.java
 1package com.bebig.hibernate.model;
 2
 3import javax.persistence.Entity;
 4import javax.persistence.GeneratedValue;
 5import javax.persistence.Id;
 6import javax.persistence.Inheritance;
 7import javax.persistence.InheritanceType;
 8
 9@Entity
10@Inheritance(strategy = InheritanceType.JOINED)
11public class Person {
12    private int id;
13
14    private String name;
15
16    @Id
17    @GeneratedValue
18    public int getId() {
19        return id;
20    }
21
22    public String getName() {
23        return name;
24    }
25
26    public void setId(int id) {
27        this.id = id;
28    }
29
30    public void setName(String name) {
31        this.name = name;
32    }
33
34}
35
其它三個文件同上。