python3 + flask + sqlalchemy +orm(3):多对多关系

一篇文章有多个tag，一个tag也可以属于多篇文章，文章和tag存在多对多关系

config.py

DEBUG = True
#dialect+driver://root:1q2w3e4r5t@127.0.0.1:3306/
DIALECT = 'mysql'
DRIVER='pymysql'
USERNAME = 'demo_user'
PASSWORD = 'demo_123'
HOST = '172.16.10.6'
PORT = 3306
DATABASE = 'db_demo1'

SQLALCHEMY_DATABASE_URI = "{}+{}://{}:{}@{}:{}/{}?charset=utf8".format(DIALECT,DRIVER,USERNAME,PASSWORD,HOST,PORT,DATABASE)
SQLALCHEMY_TRACK_MODIFICATIONS = False
print(SQLALCHEMY_DATABASE_URI)

app.py

from flask import Flask
import config

from flask_sqlalchemy import SQLAlchemy
from sqlalchemy.ext.declarative import declarative_base

app = Flask(__name__)
app.config.from_object(config)

db = SQLAlchemy(app)
Base = declarative_base()

article_tag = db.Table('article_tag',
                       db.Column('article_id',db.Integer,db.ForeignKey("article.id"),primary_key=True),
                       db.Column('tag_id',db.Integer,db.ForeignKey("tag.id"),primary_key=True)
                       )

class Article(db.Model):
    __tablename__='article'
    id = db.Column(db.Integer,primary_key=True,autoincrement=True)
    title = db.Column(db.String(100),nullable=True)
    tags = db.relationship('Tag',secondary=article_tag,backref=db.backref('articles'))

class Tag(db.Model):
    __tablename__='tag'
    id = db.Column(db.Integer,primary_key=True,autoincrement=True)
    name = db.Column(db.String(100),nullable=True)

db.create_all()

@app.route('/')
def index():
    article1 = Article(title="aaa")
    article2 = Article(title="bbb")

    tag1 = Tag(name='')
    tag2 = Tag(name='')

    article1.tags.append(tag1)
    article1.tags.append(tag2)
    article2.tags.append(tag1)
    article2.tags.append(tag2)
    db.session.add(article1)
    db.session.add(article2)
    db.session.add(tag1)
    db.session.add(tag2)
    db.session.commit()
    return 'index'

if __name__ == '__main__':
    app.run(debug=True)