model層

class Studentnew(db.Model):
    id = db.Column(db.Integer,primary_key=True)
    name = db.Column(db.String(20),unique=True)

    #新增多對多的反向引用,必須使用secondary指定中間關聯表
    courses = db.relationship('Course', secondary='xuankebiao',
                              backref=db.backref('students', lazy='dynamic'), lazy='dynamic')

class Course(db.Model):
    id = db.Column(db.Integer,primary_key=True)
    name = db.Column(db.String(20),unique=True)

# 學生選課表(中間關聯表)，不需要使用者維護
xuankebiao = db.Table('xuankebiao',
    db.Column('student_id', db.Integer, db.ForeignKey('studentnew.id')),
    db.Column('course_id', db.Integer, db.ForeignKey('course.id')),
)

views函式:

#多對多關係查詢
@blue.route('/manytomany/<id>/')
def manytumany(id):
    #根據學生找課程
    # student =Studentnew.query.get(id)
    # courses = student.courses.all()
    # return ','.join(c.name for c in courses)

    #根據課程找學生
    course = Course.query.get(id)
    stus = course.students.all()
    return ','.join((i.name for i in stus))

#多對多新增刪除
@blue.route('/many_many/')
def many_many():
    student = Studentnew.query.get(1)
    course = Course.query.get(5)
    #學生選課
    # student.courses.append(course)
    # return student.name + '選了' + course.name

    #取消選課
    student.courses.remove(course)
    return student.name + '取消' + course.name