多对一关系在同一张桌子上

Question

您认为一家公司，该公司在Users表上有员工，经理必须在Users表上。

例：

Users Table : John Watson userID=1 managerId=2(manager id have userID value)
              Emilia Clarke userID=2 managerID=null(Because this user is a Manager)

您如何看待我呢？ managerID行与Users表的多对一关系（尽管具有相同的表）

约翰·沃森（John Watson）的艾米莉亚·克拉克（Emilia Clark）经理（因为约翰的managerID，艾米莉亚的用户ID

Answer 1

只需保留userId并添加一个布尔值isManager即可，如果用户是管理员，则其值为true，否则为false。

Answer 2

要获取员工列表及其经理的详细信息，请尝试以下操作：

SELECT employee.userID,
       employee.userName,
       manager.userID,
       manager.userName
FROM Users AS employee
JOIN Users AS manager ON employee.managerID = manager.userID
ORDER BY employee.userName,
         employee.userID;

要获取经理及其员工的列表，请尝试以下操作...

SELECT manager.userID,
       manager.userName
       employee.userID,
       employee.userName,
FROM Users AS manager
JOIN Users AS employee ON manager.userID = employee.managerID
ORDER BY manager.userName,
         manager.userID,
         employee.userName,
         employee.userID;

（说明如下...）

如果您有任何问题或意见，请随时发表评论。

Answer 3

您可以如下映射：

@Entity
@Table(name = "users")
public class User {

    @Id
    @Column(name = "user_id")
    @GeneratedValue(strategy = ...)
    private Long id;

    @OneToMany(mappedBy = "manager")
    private Set<User> employees;

    @ManyToOne
    @JoinColumn(name = "manager_id"
    private User manager;
}