我收到“AttributeError：'NoneType'对象没有属性'_instantiate_plugins'”错误

Question

我有一个基于简单教程的简单 Flask 应用程序，我正在尝试将我的数据库凭据从代码中取出并放入环境变量中。我在

DB_CONNECTION_STR

中定义了

.env

，它位于我的应用程序的根目录中。以下是我的

database.py

文件的顶部。这应该是一个简单的修复；我可能遗漏了一个明显的错字。

from sqlalchemy import create_engine, text
import os

DB_CONNECTION_STR = os.environ.get('DB_CONNECTION_STR')

# These both print the right value:
print(DB_CONNECTION_STR)
print(os.environ.get('DB_CONNECTION_STR'))

# This works:
db_connection_string = "mysql+pymysql://ehcazu8mvtvv4i44ghs3:[e-mail]/joviancareers?charset=utf8mb4"

# Trying either of these two gives me a "AttributeError: 'NoneType' object has no attribute '_instantiate_plugins'"
# db_connection_string = DB_CONNECTION_STR
# db_connection_string = os.environ.get('DB_CONNECTION_STR')

engine = create_engine(db_connection_string, connect_args={
  "ssl": {
    "ca": "/etc/ssl/certs/ca-certificates.crt"
  }
})

这是我收到的错误：

Traceback (most recent call last):
  File "/home/taylor/src/jovian-carrers/app.py", line 2, in <module>
    from database import load_jobs
  File "/home/taylor/src/jovian-carrers/database.py", line 17, in <module>
    engine = create_engine(db_connection_string,
  File "<string>", line 2, in create_engine
  File "/home/taylor/src/jovian-carrers/venv/lib/python3.10/site-packages/sqlalchemy/util/deprecations.py", line 298, in warned
    return fn(*args, **kwargs)
  File "/home/taylor/src/jovian-carrers/venv/lib/python3.10/site-packages/sqlalchemy/engine/create.py", line 518, in create_engine
    u, plugins, kwargs = u._instantiate_plugins(kwargs)
AttributeError: 'NoneType' object has no attribute '_instantiate_plugins'

Answer 1

在我的头撞在墙上一个小时后，我在发布问题后立即弄清楚了。我必须将代码放置在函数内部来设置引擎，并且我假设当它位于函数外部时，它在应用程序编译时无法访问环境变量？

这不起作用：

DB_CONNECTION_STR = os.environ.get('DB_CONNECTION_STR')

db_connection_string = DB_CONNECTION_STR

engine = create_engine(db_connection_string, connect_args = {
  "ssl": {
    "ca": "/etc/ssl/certs/ca-certificates.crt"
  }
})

def load_jobs():
  with engine.connect() as conn:
    result = conn.execute(text("SELECT * FROM jobs"))
    jobs = [dict(row) for row in result.all()]
    return jobs

这可行，但需要硬编码凭据：

db_connection_string = "mysql+pymysql://ehcazu8mvtvv4i44ghs3:[e-mail]/joviancareers?charset=utf8mb4"

engine = create_engine(db_connection_string, connect_args = {
  "ssl": {
    "ca": "/etc/ssl/certs/ca-certificates.crt"
  }
})

def load_jobs():
  with engine.connect() as conn:
    result = conn.execute(text("SELECT * FROM jobs"))
    jobs = [dict(row) for row in result.all()]
    return jobs

这无需硬编码凭据即可工作：

def load_jobs():
  DB_CONNECTION_STR = os.environ.get('DB_CONNECTION_STR')
  db_connection_string = DB_CONNECTION_STR
  engine = create_engine(db_connection_string, connect_args = {
    "ssl": {
      "ca": "/etc/ssl/certs/ca-certificates.crt"
    }
  })
  with engine.connect() as conn:
    result = conn.execute(text("SELECT * FROM jobs"))
    jobs = [dict(row) for row in result.all()]
    return jobs