Flask数据库关系教程

基础配置

<pre class="python">```
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'

一对多

<pre class="python">```
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'))

多对一（不是必须时还是用与一对多吧）

比一对多的用法，会少一个从一里访问多的字段。

<pre class="python">```
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)

一对一

<pre class="python">```
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'

多对多

<pre class="python">```
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))