不使用外键实现一对多

from flask_sqlalchemy import SQLAlchemy
from flask import Flask
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///C:/Users/Administrator/Desktop/server/yh_flask/db/flask_web.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True

db = SQLAlchemy(app)


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

class Article(db.Model):
    __tablename__ = 'article'
    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    title = db.Column(db.String(100), nullable=False)
    tag = db.relationship('Tag',
                           primaryjoin='foreign(Article.id) == Tag.id',
                           backref=db.backref('articles')
                           )
    #这种写法也可以
    #tag_id = db.Column(db.Integer)
    #tag = db.relationship('Tag', foreign_keys=[tag_id],primaryjoin='Article.id == Tag.id')

@app.route('/')
def index():
    db.create_all()
    return 'create_all'

@app.route('/addData')
def addData():
    article1 = Article(title='大俸打更人')
    article2 = Article(title='雪中悍刀行')

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

    article1.tag = tag2
    article2.tag = tag1

    db.session.add(tag1)
    db.session.add(tag2)

    db.session.commit()
    return 'add_data_success'

@app.route('/queryData')
def queryData():
    article1 = Article.query.filter(Article.title == '大俸打更人').first()
    tag = article1.tag
    print(tag.name)

    t = Tag.query.filter(Tag.name == '武侠').first()
    articles = t.articles  
    for article in articles:
        print(article.title)
    return 'query_data_success'

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

不使用外键实现多对多

from flask_sqlalchemy import SQLAlchemy
from flask import Flask
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///C:/Users/Administrator/Desktop/server/yh_flask/db/flask_web.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True

db = SQLAlchemy(app)
article_tag = db.Table('article_tag',
                       db.Column('article_id', db.Integer, primary_key=True),
                       db.Column('tag_id', db.Integer, primary_key=True)
                       )

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

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

@app.route('/')
def index():
    db.create_all()
    return 'create_all'

@app.route('/addData')
def addData():
    article1 = Article(title='大俸打更人')
    article2 = Article(title='雪中悍刀行')

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

    article1.tags.append(tag1)
    article1.tags.append(tag2)

    article2.tags.append(tag1)

    db.session.add(article1)
    db.session.add(article2)

    db.session.add(tag1)
    db.session.add(tag2)

    db.session.commit()
    return 'add_data_success'

@app.route('/queryData')
def queryData():
    article1 = Article.query.filter(Article.title == '大俸打更人').first()
    tags = article1.tags
    for tag in tags:
        print(tag.name)

    t = Tag.query.filter(Tag.name == '武侠').first()
    articles = t.articles  
    for article in articles:
        print(article.title)
    return 'query_data_success'

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