[FIXED] Access to app.models from python terminal in app with Flask's Application factory

Issue

I configured the app for using Application Factories. App goes well, I can login, create users, query information from Postgres DB, Migrate tables, etc.

I used to query data from models in python console for check status and test some ORM configuration before Application Factories changes, I used to run these commands and get response

PC:~/exercises/$ python
Python 3.8.5 (default, Sep  4 2020, 07:30:14) 
>>> from app.models import *
>>> User.query.all()

After applying configuration I tried to retrieve queries. Import tables do not return any error however query returns this error:

>>> from app.models import *
>>> User.query.all()
Traceback (most recent call last):
  File "/home/dannisis/dock_exercise/emailservices/env/lib/python3.8/site-packages/sqlalchemy/util/_collections.py", line 1008, in __call__
    return self.registry[key]
KeyError: <greenlet.greenlet object at 0x7f0cb7196bf0 (otid=0x7f0cb818dd40) current active started main>

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/dannisis/dock_exercise/emailservices/env/lib/python3.8/site-packages/flask_sqlalchemy/__init__.py", line 552, in __get__
    return type.query_class(mapper, session=self.sa.session())
  File "/home/dannisis/dock_exercise/emailservices/env/lib/python3.8/site-packages/sqlalchemy/orm/scoping.py", line 129, in __call__
    return self.registry()
  File "/home/dannisis/dock_exercise/emailservices/env/lib/python3.8/site-packages/sqlalchemy/util/_collections.py", line 1010, in __call__
    return self.registry.setdefault(key, self.createfunc())
  File "/home/dannisis/dock_exercise/emailservices/env/lib/python3.8/site-packages/sqlalchemy/orm/session.py", line 4044, in __call__
    return self.class_(**local_kw)
  File "/home/dannisis/dock_exercise/emailservices/env/lib/python3.8/site-packages/flask_sqlalchemy/__init__.py", line 174, in __init__
    self.app = app = db.get_app()
  File "/home/dannisis/dock_exercise/emailservices/env/lib/python3.8/site-packages/flask_sqlalchemy/__init__.py", line 1042, in get_app
    raise RuntimeError(
RuntimeError: No application found. Either work inside a view function or push an application context. See http://flask-sqlalchemy.pocoo.org/contexts/.

I tried import models' tables with `from create_app.models import *' it returns error too. How can I retrieve queries in terminal or console

Tree application simplified and the related app configurations below:

├── app
│   ├── admin
│   │   ├── forms.py
│   │   ├── __init__.py
│   │   └── views.py
│   ├── config.py
│   ├── errors
│   │   ├── forms.py
│   │   └── __init__.py
│   ├── __init__.py
│   ├── main
│   │   ├── forms.py
│   │   ├── __init__.py
│   │   ├── utils.py
│   │   └── views.py
│   ├── models.py
│   ├── static
│   │   ├── css
│   │   │   └── styles.css
│   │   ├── img
│   │   │   └── favicon.ico
│   │   └── js
│   │       └── scripts.js
│   └── templates
│       ├── account.html
│       ├── home.html
│       ├── index.html
│       └── layout.html
├── migrations
│   ├── alembic.ini
│   ├── script.py.mako
│   └── versions
│       ├── 1de2ece5a3da_initial_commit.py
│       └── 9815b2f43f0a_tabla_dependientes.py
├── requirements.txt
├── run.py
└── tree.txt

Run file is:

from app import create_app

app = create_app()

if __name__ == "__main__":
    app.run(debug=True)

Models file simplified too is:

class User(db.Model, UserMixin):
    id = db.Column(db.Integer, primary_key=True)
    date_created = db.Column(db.DateTime, default=datetime.utcnow)
    username = db.Column(db.String(30), unique=True, nullable=False)

Init file in app directory include imports and db, migrate, bcrypt, etc instantiation and application function is

def create_app(config_class = Config):
    app = Flask(__name__)
    app.config.from_object(Config)
    app.config['SQLALCHEMY_DATABASE_URI'] = db_prefix + f'{Config.POSTGRES_DBNAME2}'

    db.init_app(app)
    migrate.init_app(app, db)
    bcrypt.init_app(app)
    login_manager.init_app(app)
    mail.init_app(app)

    from app.main.views import main
    from app.admin.views import admin
    app.register_blueprint(main)
    app.register_blueprint(admin)

    return app

Solution

Use the flask shell command to access your application. The purpose of this command is to start a Python interpreter in the context of the application. What do I mean:

$ python
>>> from app.models import *
>>> User.query.all()

# Output
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  #...

But:

$ flask shell
>>> from app.models import *
>>> User.query.all()

# Output
# ... no traceback

With a regular interpreter session, app is not known unless explicitly imported, but flask shell pre-imports your application instance.

How to configure flask shell

In your application's entry point, which is run.py, configure a shell context, which is a list of other symbols to pre-import.

# run.py

from app import create_app, db
from app.models import User

app = create_app()

@app.shell_context_processor
def make_shell_context():
    return {
            'db': db,
            'User': User
            }

if __name__ == "__main__":
    app.run(debug=True)

In your terminal, run:

$ flask shell
>>> from app.models import *
>>> User.query.all()

# Output
# ... no traceback

Answered By - Gitau Harrison