一對多關係:

class Grade(db.Model):
    id=db.Column(db.Integer,primary_key=True)
    name=db.Column(db.String(20),nullable=False)
    num = db.Column(db.Integer, default=0)
    time = db.Column(db.String(20), default='2018-01-01')

    students=db.relationship('Student',backref='gd',lazy='dynamic')
    __tablename__
 
='grade'


class Student(db.Model):
    id=db.Column(db.String(50),primary_key=True)
    name=db.Column(db.String(50),nullable=False)
    password = db.Column(db.String(50), nullable=False)
    sex = db.Column(db.String(50), nullable=False)
    phone = db.Column(db.String(11), nullable=False)
    photo 
 
= db.Column(db.String(100), default=None)

    grades=db.Column(db.Integer,db.ForeignKey('grade.id'))

    __tablename__ = 'student'

一對一關係:在relationship裡面lazy變數去掉,換成uselist=False

多對多關係:

其實多對多關係的處理是在兩個表之間建立另外一張表格,設定兩個外來鍵去分別關聯另外兩張表的主鍵

t_g=db.Table('t_g',db.Column('t_id',db.String(50),db.ForeignKey('
 
teacher.id')),db.Column('g_id',db.Integer,db.ForeignKey('grade.id')))

class Teacher(db.Model,DBO):
    id=db.Column(db.String(50),primary_key=True)
    name=db.Column(db.String(50),nullable=False)
    password = db.Column(db.String(50), nullable=False)
    phone=db.Column(db.String(11), nullable=False)
    photo=db.Column(db.String(100),default=None)

    grades=db.relationship('Grade',secondary=t_g,backref='th',lazy='dynamic')
    __tablename__='teacher'


class Grade(db.Model,DBO):
    id=db.Column(db.Integer,primary_key=True)
    name=db.Column(db.String(20),nullable=False)
    num = db.Column(db.Integer, default=0)
    time = db.Column(db.String(20), default='2018-01-01')

    students=db.relationship('Student',backref='gd',lazy='dynamic')
    __tablename__='grade'