db.create_all() 'NoneType' 对象没有属性 'drivername'

我正在关注 CS50 的使用 Python 和 Javascript 的 Web 编程，在 Lecture4 中，我在尝试创建 postgresql 数据库表时遇到以下错误：

 Traceback (most recent call last):
  File "create.py", line 19, in <module>
    main()
  File "create.py", line 15, in main
    db.create_all()
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 963, in create_all
    self._execute_for_all_tables(app, bind, 'create_all')
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 955, in _execute_for_all_tables
    op(bind=self.get_engine(app, bind), **extra)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 896, in get_engine
    return connector.get_engine()
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 556, in get_engine
    self._sa.apply_driver_hacks(self._app, info, options)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 830, in apply_driver_hacks
    if info.drivername.startswith('mysql'):
AttributeError: 'NoneType' object has no attribute 'drivername'

我使用的代码位于两个 python 文件中： 第一个名为 models.py：

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

class Flight(db.Model):
    __tablename__ = "flights"
    id = db.Column(db.Integer, primary_key=True)
    origin = db.Column(db.String, nullable=False)
    destination = db.Column(db.String, nullable=False)
    duration = db.Column(db.Integer, nullable=False)

class Passenger(db.Model):
    __tablename__ = "passengers"
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String, nullable=False)
    flight_id = db.Column(db.Integer, db.ForeignKey("flight.id"), nullable=False)

第二个文件名为 create.py：

import os

from flask import Flask, render_template, request
from models import *

app = Flask(__name__)
app.config["SQLALCHEMY_DATABASE_URI"] = os.getenv("postgresql://postgres:password@localhost/database1")
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
db.init_app(app)

def main():
    db.create_all()

if __name__ == "__main__":
    with app.app_context():
        main()

你能帮助我吗？！

我认为这是您尝试连接的方式的问题Postgres数据库：

app.config["SQLALCHEMY_DATABASE_URI"] = os.getenv("postgresql://postgres:password@localhost/database1")

您可能希望这一行改为以下内容：

app.config["SQLALCHEMY_DATABASE_URI"] = "postgresql://postgres:password@localhost/database1"

自从os.getenv(...)当前正在尝试在您的系统上获取名为：的环境变量："postgresql://postgres:password@localhost/database1"并且您肯定没有设置具有此名称的环境变量..这就是为什么您会得到一个NoneType你的错误postgres driver:

AttributeError：“NoneType”对象没有属性“drivername”。

如果您想使用环境变量来获取数据库连接字符串，请在您的.bash_profile or .bashrc file:

export SQLALCHEMY_DATABASE_URI='postgresql://postgres:password@localhost/database1'

然后将数据库连接代码更改为以下内容：

app.config["SQLALCHEMY_DATABASE_URI"] = os.environ.get('SQLALCHEMY_DATABASE_URI')

希望这是有道理的！