Flask database relationships

Basic Configuration

from flask import Flask
from flask_sqlalchemy import SQLAlchemy


app = Flask(__name__)
db = SQLAlchemy(app)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql+pymysql://root:root@localhost/flask'

Many

class Singer(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(70), unique=True)
    songs = db.relationship('Song', backref='singer')

class Song(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(70), unique=True)
    singer_id = db.Column(db.Integer, db.ForeignKey('singer.id'))

Many-to (or have to use and when not many bars)

Than the use of one-to-one less mile access from many fields.

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 Country(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(79), unique=True)
    capital = db.relationship('Capital', uselist=False)

One to One

class Country(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(79), 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(70), unique=True)
    country_id = db.Column(db.Integer, db.ForeignKey('country.id'))
    country = db.relationship('Country'

Many to many

association_table = db.Table(
    'association',
    db.Column('student_id', db.Integer, db.ForeignKey('student.id')),
    db.Column('teacher_id', db.Integer, db.ForeignKey('teacher.id'))
)


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, backref='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))