首先创建多对多关系代码

# 假设有两个实体：学生和课程
# 学生实体
class Student:
    def __init__(self, student_id, name):
        self.student_id = student_id
        self.name = name
        self.courses = []  # 学生所选的课程列表

    def enroll_course(self, course):
        self.courses.append(course)

    def get_courses(self):
        return self.courses

# 课程实体
class Course:
    def __init__(self, course_id, name):
        self.course_id = course_id
        self.name = name
        self.students = []  # 选修该课程的学生列表

    def add_student(self, student):
        self.students.append(student)

    def get_students(self):
        return self.students

# 创建学生和课程实例
student1 = Student(1, "张三")
student2 = Student(2, "李四")
course1 = Course(1, "数学")
course2 = Course(2, "英语")

# 建立多对多关系
student1.enroll_course(course1)
student1.enroll_course(course2)
student2.enroll_course(course1)

course1.add_student(student1)
course1.add_student(student2)
course2.add_student(student1)

# 获取学生所选的课程
print(student1.get_courses())  # 输出: [course1, course2]
print(student2.get_courses())  # 输出: [course1]

# 获取选修某门课程的学生
print(course1.get_students())  # 输出: [student1, student2]
print(course2.get_students())  # 输出: [student1]