Flask with SQLAlchemy working outside of application context - flask

Question

I have a Flask app and I use SQLAlachemy(without Flask extension cause I need to create my own class based SQLAlchemy and so on).
My app has a connection to its database over engine and it works fine but now I need to make my engine dynamically and get db_name from Flask.g
Engine is declared in models.py
models.py
engine = create_engine(f"postgresql://postgres:postgres#localhost:5434/{g['tenant']}", convert_unicode=True)
db_session = scoped_session(sessionmaker(autocommit=False,
autoflush=False,
bind=engine))
Base = declarative_base()
Base.query = db_session.query_property()
For the start app I use wsgi.py:
from app import app
if __name__ == "__main__":
app.run(port=5002)
when I type python wsgi.py I receive an error.
RuntimeError: Working outside of application context.
This typically means that you attempted to use functionality that needed
to interface with the current application object in some way. To solve
this, set up an application context with app.app_context(). See the
documentation for more information.
In general I understand that I use an engine which is outside the context. The issue is - I cannot figure out how to pass my engine variable to context.
I try to make create app func:
def create_app():
app = Flask(__name__)
with app.app_context():
engine = create_engine(f"postgresql://postgres:postgres#localhost:5434/{g['tenant']}", convert_unicode=True)
return app
Also I tried app.app_context().push(engine)
But it doesn't work. How I can solve this issue?

Answer 1

The problem is that the flask object g only ever exists when a request is currently in progress on flask. (Without a request, there is no flask g, because g is specifically a global for individual requests)
what you'd have to do is to create that engine after the request starts, which slows down the route a bit. The #app.before_request decorator might help you here:
#app.before_request
def create_engine_for_request():
engine = create_engine(f"postgresql://postgres:postgres#localhost:5434/{g['tenant']}", convert_unicode=True)
("before_request" is already "during a request" - its just the first thing that flask does "when a request starts")