我正在Flask-SQLAlchemy中构建以下数据库方案:
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from datetime import datetime
app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db'
db = SQLAlchemy(app)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(64), index=True, unique=True)
email = db.Column(db.String(120), index=True, unique=True)
password_hash = db.Column(db.String(128))
posts = db.relationship('Post', backref='author', lazy='dynamic')
def __repr__(self):
return '<User {}>'.format(self.username)
class Post(db.Model):
id = db.Column(db.Integer, primary_key=True)
body = db.Column(db.String(140))
timestamp = db.Column(db.DateTime, index=True, default=datetime.utcnow)
user_id = db.Column(db.Integer, db.ForeignKey('user.id'))
def __repr__(self):
return '<Post {}>'.format(self.body)
db.drop_all()
db.create_all()
u = User(username='susan', email='susan@example.com')
db.session.add(u)
p = Post(body='this is my first post!', user_id=1)
db.session.add(p)
# Now I create a new post for a non-existing user and I'd expect an error...
p = Post(body='this is my second post!', user_id=2)
db.session.add(p)
db.session.commit()
如您所见,我手动输入一个新用户,然后输入两个帖子。
我想在第二篇文章中插入错误,因为数据库中不存在user_id = 2。
但是插入成功,并且我还看到了数据进入数据库:
sqlite> select * from post;
1|this is my post!|2018-07-09 16:13:16.947856|1
2|this is my post!|2018-07-09 16:13:16.948996|2
sqlite>
如何强制约束以使其引发错误?
感谢您的帮助。
答案 0 :(得分:1)
要解决这种情况,与其将id分配给post对象,不如将User与Post关联起来更像ORM。另外,通过强制使用外键列的npm install npm-conf@1.1.0
功能,不能添加无效数字。
例如:
NOT NULL