shop_platform - flask db init fails: KeyError 'migrate'

試著使用 Flask-Migrate 做 MySQL 的 migration。但是在終端機使用 flask db init 指令時失敗了。

程式碼：

common/database.py：

from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate


db = SQLAlchemy()
migrate = Migrate()

app.py：

import os
from flask import Flask
from dotenv import load_dotenv
from common.database import db, migrate


if os.environ.get('FLASK_ENV', '') != 'production':
    load_dotenv()

app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_DATABASE_URI'] = os.environ.get('SQLALCHEMY_DATABASE_URI')


@app.route('/')
def home():
    return 'Hello World!'

if __name__ == '__main__':
    db.init_app(app)
    migrate.init_app(app, db)
    app.run()

錯誤訊息：

  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/bin/flask", line 8, in <module>
    sys.exit(main())
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/flask/cli.py", line 990, in main
    cli.main(args=sys.argv[1:])
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/flask/cli.py", line 596, in main
    return super().main(*args, **kwargs)
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/click/core.py", line 1062, in main
    rv = self.invoke(ctx)
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/click/core.py", line 1668, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/click/core.py", line 1668, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/click/core.py", line 763, in invoke
    return __callback(*args, **kwargs)
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/click/decorators.py", line 26, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/flask/cli.py", line 440, in decorator
    return __ctx.invoke(f, *args, **kwargs)
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/click/core.py", line 763, in invoke
    return __callback(*args, **kwargs)
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/flask_migrate/cli.py", line 45, in init
    _init(directory, multidb, template, package)
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/flask_migrate/__init__.py", line 98, in wrapped
    f(*args, **kwargs)
  File "/Users/flora/.local/share/virtualenvs/shop_platform-9-YKR-2e/lib/python3.9/site-packages/flask_migrate/__init__.py", line 122, in init
    directory = current_app.extensions['migrate'].directory
KeyError: 'migrate'

最後找到這篇文章：flask_migrate KeyError: 'migrate'

雖然還不是很明白背後的原理是什麼，但是，大概是，如果有用 application factory，那麼就搭配使用

db.init_app(app)
migrate.init_app(app, db)

如果沒有用 application factory，那麼就搭配使用

db = SQLAlchemy(app)
migrate = Migrate(app, db)

我是因為沒有用 application factory，卻又使用了 db.init_app(app)、migrate.init_app(app, db)，所以才出錯。

commit: fix: KeyError when execute flask db init