使用 Flask-SQLAlchemy 反射表会引发 RuntimeError：应用程序未注册

Question

我有一个 SQLite 数据库来管理用户登录，以及一个现有的 MySQL 数据库。我将 MySQL 数据库添加到 Flask-SQLAlchemySQLALCHEMY_BINDS配置中。当我尝试反映表格时，出现以下错误：

RuntimeError: application not registered on db instance and no application bound to current context

如何正确反映表格？

__init__.py：

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
from config import config

db = SQLAlchemy()

def create_app(config_name):
    app = Flask(__name__)
    app.config.from_object(config[config_name])
    config[config_name].init_app(app)

    db.init_app(app)

    from .main import main as main_blueprint
    app.register_blueprint(main_blueprint)

    return app

manage.py：

from myapp import create_app
from flask.ext.migrate import Migrate, MigrateCommand

app = create_app(os.getenv('FLASK_CONFIG') or 'default')
manager = Manager(app)
migrate = Migrate(app, db)
manager.add_command('db', MigrateCommand)

if __name__ == '__main__':
    manager.run()

models.py：

from . import db, login_manager

db.Model.metadata.reflect(db.engine)

class Calls(db.Model):
    __table__ = db.Model.metadata.tables['Calls2']
    __bind_key__ = 'calls'

    def __repr__(self):
        return self.test1

Traceback (most recent call last):
  File "./manage.py", line 6, in <module>
    from app.models import User, Role, Permission
  File "/home/ilias/Desktop/client-reporting/app/models.py", line 9, in <module>
    db.Model.metadata.reflect(db.engine)
  File "/home/ilias/Desktop/client-reporting/local/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py", line 780, in engine
    return self.get_engine(self.get_app())
  File "/home/ilias/Desktop/client-reporting/local/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py", line 809, in get_app
    raise RuntimeError('application not registered on db '
RuntimeError: application not registered on db instance and no application bound to current context

Answer 1

在使用应用程序初始化扩展程序之前，您无法对数据库执行操作，这在使用应用程序工厂函数之前不会发生。reflect在工厂内部移动调用，并使用db.reflect，它反映了所有绑定，而不仅仅是主要绑定。

def create_app():
    app = Flask(__name__)
    ...

    db.init_app(app)
    db.reflect(app=app)
    # you could also push an app context instead of passing app
    # with app.app_context():
    #     db.reflect()

    ...
    return app

由于模型是作为视图的一部分导入的，这些视图仅在工厂内部导入，因此元数据将在定义模型时包含反映的表。