// Department.java (一方)
@Entity
public class Department {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    
    @OneToMany(mappedBy = "department", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<Employee> employees = new ArrayList<>();
    
    // 辅助方法，用于维护双向关系
    public void addEmployee(Employee employee) {
        employees.add(employee);
        employee.setDepartment(this);
    }
    
    public void removeEmployee(Employee employee) {
        employees.remove(employee);
        employee.setDepartment(null);
    }
    
    // getters and setters
}

// Employee.java (多方)
@Entity
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    
    @ManyToOne
    @JoinColumn(name = "department_id")
    private Department department;
    
    // getters and setters
}

// Student.java
@Entity
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    
    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    @JoinTable(name = "student_course",
        joinColumns = @JoinColumn(name = "student_id"),
        inverseJoinColumns = @JoinColumn(name = "course_id"))
    private List<Course> courses = new ArrayList<>();
    
    // 辅助方法
    public void addCourse(Course course) {
        courses.add(course);
        course.getStudents().add(this);
    }
    
    public void removeCourse(Course course) {
        courses.remove(course);
        course.getStudents().remove(this);
    }
    
    // getters and setters
}

// Course.java
@Entity
public class Course {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    
    @ManyToMany(mappedBy = "courses")
    private List<Student> students = new ArrayList<>();
    
    // getters and setters
}