When scattering Flask Models, RuntimeError: 'application not registered on db' was raised
Question:
I am re-factoring my Flask application by scattering the models, blueprints but I am having a runtime error.
def create_app():
app = flask.Flask("app")
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite://'
app.register_blueprint(api)
db.init_app(app)
db.create_all()
return app
I have the following problem(the sample project are hosted here: https://github.com/chfw/sample):
Traceback (most recent call last):
File "application.py", line 17, in <module>
app = create_app()
File "application.py", line 12, in create_app
db.create_all()
File "AppDataRoamingPythonPython27site-packagesflask_sqlalchemy__init__.py", line 856, in create_all
self._execute_for_all_tables(app, bind, 'create_all')
File "AppDataRoamingPythonPython27site-packagesflask_sqlalchemy__init__.py", line 836, in _execute_for_all_tables
app = self.get_app(app)
File "AppDataRoamingPythonPython27site-packagesflask_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
I did a research on this topic. The re-factoring is suggested here:
Flask-SQLAlchemy import/context issue
The same problem was raised here:
And the above thread(2010) suggested a hack like this:
app.register_blueprint(api)
db.app=app #<------------<<
db.init_app(app)
Did anyone know how to do this properly? How did you solve it?
Thanks
Answers:
This has to do with Flask’s application context. When initialized with db.init_app(app)
, Flask-SQLAlchemy doesn’t know which app is the “current” app (remember, Flask allows for multiple apps in the same interpreter). You could have multiple apps using the same SQLAlchemy
instance in the same process, and Flask-SQLAlchemy would need to know which is the “current” one (due to Flask’s context local nature of everything).
If you need to do this during runtime, you must explicitly say which app is the “current” app for all calls. You can do this by changing your code to use a with app.app_context()
block:
def create_app():
app = flask.Flask("app")
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite://'
app.register_blueprint(api)
db.init_app(app)
with app.app_context():
# Extensions like Flask-SQLAlchemy now know what the "current" app
# is while within this block. Therefore, you can now run........
db.create_all()
return app
If you are writing a standalone script that needs the app context, you can push the context at the beginning rather than putting everything in a with
block.
create_app().app_context().push()
If you write a command for Flask’s cli the command will automatically have access to the context.
Mark’s answer was great and it helped me a lot. However, another way to approach this is to run the code that relies on the app context in a function decorated with @app.before_first_request. See http://flask.pocoo.org/docs/0.10/appcontext/ for more information. That’s in fact how I ended up doing it, largely because I wanted to be able to call the initialization code outside of flask as well, which I handle this way.
In my case I want to be able to test SQLAlchemy models as plain SQLAlchemy models without Flask-SQLAlchemy, though the db in the code below is simply a (Flask) SQLAlchemy db.
@app.before_first_request
def recreate_test_databases(engine = None, session = None):
if engine == None:
engine = db.engine
if session == None:
session = db.session
Base.metadata.drop_all(bind=engine)
Base.metadata.create_all(bind=engine)
# Additional setup code
I am re-factoring my Flask application by scattering the models, blueprints but I am having a runtime error.
def create_app():
app = flask.Flask("app")
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite://'
app.register_blueprint(api)
db.init_app(app)
db.create_all()
return app
I have the following problem(the sample project are hosted here: https://github.com/chfw/sample):
Traceback (most recent call last):
File "application.py", line 17, in <module>
app = create_app()
File "application.py", line 12, in create_app
db.create_all()
File "AppDataRoamingPythonPython27site-packagesflask_sqlalchemy__init__.py", line 856, in create_all
self._execute_for_all_tables(app, bind, 'create_all')
File "AppDataRoamingPythonPython27site-packagesflask_sqlalchemy__init__.py", line 836, in _execute_for_all_tables
app = self.get_app(app)
File "AppDataRoamingPythonPython27site-packagesflask_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
I did a research on this topic. The re-factoring is suggested here:
Flask-SQLAlchemy import/context issue
The same problem was raised here:
And the above thread(2010) suggested a hack like this:
app.register_blueprint(api)
db.app=app #<------------<<
db.init_app(app)
Did anyone know how to do this properly? How did you solve it?
Thanks
This has to do with Flask’s application context. When initialized with db.init_app(app)
, Flask-SQLAlchemy doesn’t know which app is the “current” app (remember, Flask allows for multiple apps in the same interpreter). You could have multiple apps using the same SQLAlchemy
instance in the same process, and Flask-SQLAlchemy would need to know which is the “current” one (due to Flask’s context local nature of everything).
If you need to do this during runtime, you must explicitly say which app is the “current” app for all calls. You can do this by changing your code to use a with app.app_context()
block:
def create_app():
app = flask.Flask("app")
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite://'
app.register_blueprint(api)
db.init_app(app)
with app.app_context():
# Extensions like Flask-SQLAlchemy now know what the "current" app
# is while within this block. Therefore, you can now run........
db.create_all()
return app
If you are writing a standalone script that needs the app context, you can push the context at the beginning rather than putting everything in a with
block.
create_app().app_context().push()
If you write a command for Flask’s cli the command will automatically have access to the context.
Mark’s answer was great and it helped me a lot. However, another way to approach this is to run the code that relies on the app context in a function decorated with @app.before_first_request. See http://flask.pocoo.org/docs/0.10/appcontext/ for more information. That’s in fact how I ended up doing it, largely because I wanted to be able to call the initialization code outside of flask as well, which I handle this way.
In my case I want to be able to test SQLAlchemy models as plain SQLAlchemy models without Flask-SQLAlchemy, though the db in the code below is simply a (Flask) SQLAlchemy db.
@app.before_first_request
def recreate_test_databases(engine = None, session = None):
if engine == None:
engine = db.engine
if session == None:
session = db.session
Base.metadata.drop_all(bind=engine)
Base.metadata.create_all(bind=engine)
# Additional setup code