flask_sqlalchemy一对一、一对多、多对一、多对多

一对多

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class Country(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(30), unique=True)
    capital = db.relationship('Capital', uselist=False)

class Capital(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(30), unique=True)
    country_id = db.Column(db.Integer, db.ForeignKey('country.id'))
    country = db.relationship('Country')

一对多

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class Author(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(70), unique=True)
    phone = db.Column(db.String(20))

class Article(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(50), index=True)
    body =	db.Column(db.Text)

多对一

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class Citizen(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(70), unique=True)
    city_id = db.Column(db.Integer, db.ForeignKey('city.id'))
    city = db.relationship('City')

class City(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(30), unique=True)

多对多

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association_table = db.Table('association',db.Column('student_id', db.Integer, db.Foreign)

class Student(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(70), unique=True)
    grade = db.Column(db.String(20))
    teachers = db.relationship('Teacher',
    secondary=association_table, back_populates='students')

class Teacher(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(70), unique=True)
    office = db.Column(db.String(20))