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

Question

我正在学习 CS50 的 Web Programming with Python and Javascript，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'

我使用的代码在两个 python 文件中:第一个叫做 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)

第二个文件叫做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()

你能帮帮我吗？!

Answer 1

我认为这是您尝试连接到 Postgres 数据库的方式的问题:

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

您可能希望这一行变成以下内容:

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

因为 os.getenv(...) 当前正在尝试在您的系统上获取一个名为:"postgresql://postgres:password@localhost/database1" 并且您肯定没有使用此名称设置环境变量。这就是您的 postgres 驱动程序出现 NoneType 错误的原因:

AttributeError: 'NoneType' object has no attribute '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 或 .bashrc 文件中执行类似以下操作:

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

然后将您的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!