Flask-SQLAlchemy 数据库一对多

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
import config
app = Flask(__name__)
app.config.from_object(config)
db=SQLAlchemy(app)

class Writer(db.Model):
    __tablename__='writer'
    id = db.Column(db.Integer,primary_key=True)
    name = db.Column(db.String(50),nullable=False)
    books = db.relationship('Book',backref='writers')
class Book(db.Model):
    __tablename__='books'
    id=db.Column(db.Integer,primary_key=True)
    title=db.Column(db.String(50),nullable=False)
    publishing_office=db.Column(db.String(100),nullable=False)
    isbn = db.Column(db.String(50),nullable=False)
    writer_id = db.Column(db.Integer,db.ForeignKey('writer.id'))
db.create_all()
@app.route('/add')
def add():
    user1 = Writer(name='李兴华')
    user2 = Writer(name='Sweigart')
    db.session.add(user1)
    db.session.add(user2)
    book1 = Book(title='名师讲坛——java开发实战经典（第2版）',publishing_office='清华大学出版社',
                 isbn='9787302483663',writer_id='1')
    book2=Book(title='android开发实战',publishing_office='清华大学出版社',
                 isbn='9787302483663',writer_id='1')
    book3=Book(title='Python游戏编程',publishing_office='人民邮电大学出版社',
                 isbn='9787151466419',writer_id='2')
    db.session.add(book1)
    db.session.add(book2)
    db.session.add(book3)
    db.session.commit()
    return '数据添加成功'
@app.route('/select')
def select():
    writer = Writer.query.filter(Writer.id=='1').first()
    book = writer.books
    for k in book:
        print(k)
        print(k.title)
    book=Book.query.filter(Book.id=='1').first()
    writer=book.writers
    print(writer.name)
    return '查询数据成功'
@app.route('/')
def hello_world():
    return "Hello world!"
if __name__ == '__main__':
    app.run()