JPA基礎（十四）：JPA中的繼承映射關係

Employee.java:(基類)

 1 @Entity
 2 @Inheritance(strategy=InheritanceType.SINGLE_TABLE)//選擇繼承策略
 3 @DiscriminatorColumn(name="type")//配置鑒別器
 4 @DiscriminatorValue("0")//設定鑒別器值
 5 public class Employee {
 6     @Id
 7     @GeneratedValue
 8     private Integer id;
 9     private String name;
10     public Integer getId() {
11         return id;
12     }
13     public void setId(Integer id) {
14         this.id = id;
15     }
16     public String getName() {
17         return name;
18     }
19     public void setName(String name) {
20         this.name = name;
21     }
22 }

其中@Inheritance(strategy=InheritanceType.SINGLE_TABLE)//選擇繼承策略 可以選擇多種策略，如所示：

• JOINED：繼承的子類各自產生一張表
• SINGLE_TABLE：只產生一張表，用一個欄位當鑒別器
• TABLE_PER_CLASS：每個類都生產一張表，包括基類

 

Skiller.java(繼承自Employee.java)

 1 @Entity
 2 @DiscriminatorValue("1")
 3 public class Skiller extends Employee {
 4     private String skill;
 5 
 6     public String getSkill() {
 7         return skill;
 8     }
 9 
10     public void setSkill(String skill) {
11         this.skill = skill;
12     }
13 }

Sales.java(繼承自Employee.java)

 1 @Entity
 2 @DiscriminatorValue("2")
 3 public class Sales extends Employee {
 4     private String sell;
 5     public String getSell() {
 6         return sell;
 7     }
 8     public void setSell(String sell) {
 9         this.sell = sell;
10     }
11 }

測試：

 1     @Test
 2     public void save(){
 3         EntityManagerFactory factory=Persistence.createEntityManagerFactory("sample");
 4         EntityManager em=factory.createEntityManager();
 5         em.getTransaction().begin();
 6         Employee p1=new Employee();
 7         p1.setName("Jim");
 8         Skiller p2=new Skiller();
 9         p2.setName("Hanson");
10         p2.setSkill("skill");
11         Sales p3=new Sales();
12         p3.setName("Brian");
13         p3.setSell("sale");
14         em.persist(p1);
15         em.persist(p2);
16         em.persist(p3);
17         em.getTransaction().commit();
18         em.close();
19         factory.close();
20     }

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