flask报错 AttributeError: 'NoneType' object has no attribute 'metadata'

• flask数据库迁移时，报错：

(venv) D:\000flask>flask db migrate
Traceback (most recent call last):
	......
	File "migrations\env.py", line 27, in <module>
    target_metadata = current_app.extensions['migrate'].db.metadata
AttributeError: 'NoneType' object has no attribute 'metadata'

• 代码如下：

db = SQLAlchemy()
migrate = Migrate()

def create_app(object_name):
	app = Flask(__name__)
	db.init_app(app)
    migrate.init_app(app)
  
    return app

• 原因：

migrate对象初始化时db也应作为参数传入

migrate.init_app(app,db)