我是Python的新手。我正在使用Flask和SQLAlchemy创建一个API。我正在寻找将 SQLAlchemy 代码拆分为模块的建议/解决方案。我正在尝试使用以下方法模块化我的代码：
/models将包含我的 SQLAlchemy 模型/methods将包含各种数据库方法，例如创建、更新和删除用户/routes将包含我的烧瓶路由处理程序
我引用了这个关于如何拆分SQLAlchemy声明性模型的堆栈溢出问题，它在一定程度上有效。使用下面显示的文件结构，我能够成功地将与数据库相关的代码拆分为所需的模块。
Directories are denoted with a leading '/'
/my_root_directory
|__ main.py Imports my Flask app and runs it
|__ /server
|__ __init__.py Imports my Flask app and database modules
|__ app.py Contains my Flask app
|__ /database
|__ __init__.py Imports initialize_database()
|__ engine.py Contains SQLAlchemy's create_engine()
|__ base.py Contains SQLAlchemy's declarative_base()
|__ session.py Contains SQLAlchemy's scoped_session(sessionmaker())
|__ initialize_database.py Contains initialize_database()
|__ /models
|__ __init__.py Imports my SQLAlchemy User model
|__ user.py Contains my SQLAlchemy User model
|__ /methods
|__ __init__.py Imports create_user()
|__ create_user.py Contains create_user()
|__ /routes
|__ __init__.py Imports my Flask route handler
|__ /api
|__ users_router.py Contains my Flask route handler for /api/v1/users
这是我的申请流程。我通过在终端中运行python main.py来执行main.py，其中包含以下代码：
main.py
from server.app import app
import os
if __name__ == "__main__":
debug = os.getenv("ENV") == "dev"
app.run(debug=debug)
在/server/__init__.py中，我执行(？)所有与数据库相关的代码：
/服务器/__init__.py
from .app import app
from .database import *
/server/database/__init__.py初始化数据库并测试我的数据库方法：
/服务器/数据库/__init__.py
from .initialize_database import initialize_database
from .methods.create_user import create_user
initialize_database()
print(create_user("jack"))
print(create_user("john"))
这成功地在我的数据库中创建新用户。下面是这两个函数的代码。为了完整起见，我还提供了包含Session和User的代码：
/服务器/数据库/initialize_database.py
from .engine import engine
from .base import Base
import os
def initialize_database():
if os.getenv("ENV") == "dev":
Base.metadata.drop_all(bind=engine)
Base.metadata.create_all(bind=engine)
/server/database/methods/create_user.py
from ..session import Session
from ..models import User
def create_user(name):
user = User(twitch_username=name)
Session.add(user)
Session.commit()
return "Created new user"
/服务器/数据库/会话.py
from sqlalchemy.orm import scoped_session, sessionmaker
from .engine import engine
Session = scoped_session(sessionmaker(bind=engine))
/服务器/数据库/模型/用户.py
from sqlalchemy import Column, String
from ..base import Base
# These SQLAlchemy model mixins don't depend on any relative modules
from .mixins import AutoUUIDMixin, TimeStampMixin
class User(Base, AutoUUIDMixin, TimeStampMixin):
__tablename__ = "users"
twitch_username = Column("twitch_username", String(50), unique=True)
def __init__(self, twitch_username):
self.twitch_username = twitch_username
但是，当我尝试通过以下方式将create_user()导入路由处理程序时：
/server/routes/api/users_router.py
from ...database.methods import create_user as CreateUser
我收到以下错误：
Traceback (most recent call last):
File "main.py", line 1, in <module>
from server.app import app
File "~/root_dir/server/__init__.py", line 1, in <module>
from .app import app
File "~/root_dir/server/app.py", line 9, in <module>
from .routes import users_router
File "~/root_dir/server/routes/__init__.py", line 1, in <module>
from .api import users_router
File "~/root_dir/server/routes/api/__init__.py", line 1, in <module>
from .users_router import users_router
File "~/root_dir/server/routes/api/users_router.py", line 2, in <module>
from ...database.methods import create_user as CreateUser
File "~/root_dir/server/database/__init__.py", line 1, in <module>
from .initialize_database import initialize_database
File "~/root_dir/server/database/initialize_database.py", line 1, in <module>
from .engine import engine
File "~/root_dir/server/database/engine.py", line 3, in <module>
engine = create_engine(os.getenv("DATABASE_URL"))
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/sqlalchemy/engine/__init__.py", line 479, in create_engine
return strategy.create(*args, **kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/sqlalchemy/engine/strategies.py", line 56, in create
plugins = u._instantiate_plugins(kwargs)
AttributeError: 'NoneType' object has no attribute '_instantiate_plugins'
如何成功模块化与数据库相关的逻辑以供 Flask 应用程序使用？我对任何方法和解决方案都持开放态度，即使这意味着完全重组我的代码库。我对 Python 模块和脚本没有最好的理解，所以如果可能的话，解释为什么我当前的文件结构没有按预期工作将非常有帮助。
以下是我的依赖项列表：
Python 3.7.4
Anaconda 4.8.3
要求.txt
click==7.1.1
Flask==1.1.2
Flask-SQLAlchemy==2.4.1
gunicorn==20.0.4
itsdangerous==1.1.0
Jinja2==2.11.1
MarkupSafe==1.1.1
psycopg2==2.8.5
psycopg2-binary==2.8.5
python-dotenv==0.12.0
SQLAlchemy==1.3.15
Werkzeug==1.0.1
环境.yml
name: flask-server
channels:
- defaults
dependencies:
- ca-certificates=2020.1.1=0
- libcxx=4.0.1=hcfea43d_1
- libcxxabi=4.0.1=hcfea43d_1
- libedit=3.1.20181209=hb402a30_0
- libffi=3.2.1=h475c297_4
- ncurses=6.2=h0a44026_0
- openssl=1.1.1f=h1de35cc_0
- pip=20.0.2=py37_1
- python=3.7.6=h359304d_2
- readline=7.0=h1de35cc_5
- setuptools=46.1.3=py37_0
- sqlite=3.31.1=ha441bb4_0
- tk=8.6.8=ha441bb4_0
- wheel=0.34.2=py37_0
- xz=5.2.4=h1de35cc_4
- zlib=1.2.11=h1de35cc_3
- pip:
- click==7.1.1
- flask==1.1.2
- flask-sqlalchemy==2.4.1
- gunicorn==20.0.4
- itsdangerous==1.1.0
- jinja2==2.11.1
- markupsafe==1.1.1
- psycopg2==2.8.5
- psycopg2-binary==2.8.5
- python-dotenv==0.12.0
- sqlalchemy==1.3.15
- werkzeug==1.0.1
编辑：这是engine.py中的代码。
/服务器/数据库/引擎.py
from sqlalchemy import create_engine
import os
print(os.getenv(“DATABASE_URL”))
# Sometimes prints None and other times prints “postgresql://localhost:5432/<my-db>“
engine = create_engine(os.getenv(“DATABASE_URL”))
在翻转代码执行后，我设法使文件结构正常工作。我不是先创建我的 Flask 应用程序，而是执行我的数据库逻辑。
/服务器/__init__.py
from .app import app
from .database import *
成为
from .database import *
from .app import app
我还在engine.py内部添加了load_dotenv().
from sqlalchemy import create_engine
from dotenv import load_dotenv
import os
load_dotenv()
print(os.getenv("DATABASE_URL"))
# Prints “postgresql://localhost:5432/<my-db>“
engine = create_engine(os.getenv("DATABASE_URL"))