使用非SQLAlchemy创建的表的外键创建模型

Question

我的烧瓶应用程序有一个我使用mysqlconnector创建的表：

import mysql.connector
from .config import host, user, passwd, db_name
connection_pool = mysql.connector.pooling.MySQLConnectionPool(
pool_size=8,
host=host,
user=user,
password=passwd,
database=db_name)
connection_object = connection_pool.get_connection()
cursor = connection_object.cursor(buffered=True)
cursor.execute(
"""CREATE TABLE IF NOT EXISTS MyTable (
ID INT AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(255) NOT NULL UNIQUE
)"""
connection_object.commit()

我正在导入的库(authlib(使用SQL 连接到同一个数据库

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from authlib.integrations.sqla_oauth2 import OAuth2ClientMixin
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql+mysqlconnector://user:pwd@host/db'
db = SQLAlchemy (app)
class OAuth2Client(db.Model, OAuth2ClientMixin):
__tablename__ = 'oauth2_client'
id = db.Column(db.Integer, primary_key=True)
smthg_id = db.Column(
db.Integer, db.ForeignKey('MyTable.id', ondelete='CASCADE'))
smthg = db.relationship('MyTable')
client = OAuth2Client()
db.session.add (client)
db.session.commit()

在执行过程中，它会引发以下错误：

sqlalchemy.exc.InvalidRequestError: When initializing mapper mapped class OAuth2Client->oauth2_client, expression 'MyTable' failed to locate a name ("name 'MyTable' is not defined"). If this is a class name, consider adding this relationship() to the <class '__main__.OAuth2Client'> class after both dependent classes have been defined.

如何在SQL Alchemy中创建包含这样一个外键的表？

Answer 1

您可以使用SQLAlchemy的反射功能为现有类创建一个Table实例，然后将该实例分配给模型的__table__属性：

import sqlalchemy as sa
...
# Load the existing table into the db object's metadata
mytable = sa.Table('MyTable', db.metadata, autoload_with=db.engine)

# Create a model over the table.
class MyTable(db.Model):
__table__ = mytable

现在CCD_ 2可以在CCD_ 3模型中被成功引用。