休眠：单表中的父子关系

您在这里表达两个概念：

1. 继承，并且您想要在单个表中映射继承层次结构。
2. 父母/子女关系。

要实现1.，您需要使用每个类层次结构策略的Hibernate
单个表：

@Entity@Inheritance(strategy=InheritanceType.SINGLE_TABLE)@DiscriminatorColumn(    name="emptype",    discriminatorType=DiscriminatorType.STRING)public abstract class Employee { ... }@Entity@DiscriminatorValue("MGR")public class Manager extends Employee { ... }

要实现2.，您需要在上添加两个自引用关联

Employee

• 许多员工有零个或一个经理（也是

  Employee

  ）
• 一名员工的报告人为零或很多

结果

Employee

@Entity@Inheritance(strategy=InheritanceType.SINGLE_TABLE)@DiscriminatorColumn(    name="emptype",    discriminatorType=DiscriminatorType.STRING)public abstract class Employee {    ...    private Employee manager;    private Set<Employee> reportees = new HashSet<Employee>();    @ManyToOne(optional = true)    public Employee getManager() {        return manager;    }    @oneToMany    public Set<Employee> getReportees() {        return reportees;    }    ...}

这将导致下表：

CREATE TABLE EMPLOYEE_EMPLOYEE (        EMPLOYEE_ID BIGINT NOT NULL,        REPORTEES_ID BIGINT NOT NULL    );CREATE TABLE EMPLOYEE (        EMPTYPE VARCHAr(31) NOT NULL,        ID BIGINT NOT NULL,        NAME VARCHAr(255),        MANAGER_ID BIGINT    );ALTER TABLE EMPLOYEE ADD ConSTRAINT SQL100311183749050 PRIMARY KEY (ID);ALTER TABLE EMPLOYEE_EMPLOYEE ADD ConSTRAINT SQL100311183356150 PRIMARY KEY (EMPLOYEE_ID, REPORTEES_ID);ALTER TABLE EMPLOYEE ADD ConSTRAINT FK4AFD4ACE7887BF92 FOREIGN KEY (MANAGER_ID)    REFERENCES EMPLOYEE (ID);ALTER TABLE EMPLOYEE_EMPLOYEE ADD ConSTRAINT FKDFD1791F25AA2BE0 FOREIGN KEY (REPORTEES_ID)    REFERENCES EMPLOYEE (ID);ALTER TABLE EMPLOYEE_EMPLOYEE ADD ConSTRAINT FKDFD1791F1A4AFCF1 FOREIGN KEY (EMPLOYEE_ID)    REFERENCES EMPLOYEE (ID);