If you are not familiar with SQLAlchemy, check out my article Getting Started with SQLAlchemy.

Flask uses the MVC (Model View Controller) Framework. Just to make this as obvious as possible, I like my Flask apps to have the following.

• Model -> models.py
• View -> views.py
• Controller -> __init__.py

And let's say your Flask app has the following structure.

├── main.py
├── database (directory)
│   ├── example.db
├── my-project (directory)
│   ├── __init__.py
│   ├── views.py
│   ├── models.py
│   ├── templates (directory)
│   │   ├── base.html
│   │   ├── home.html
│   │   ├── results.html
│   └── static (directory)
│       └── custom.css

You will need to install the psycopg module to be able to make the connection to Postgres.

pip install flask-sqlalchemy
pip install psycopg2

Or, you can specify the version to install

pip install flask-sqlalchemy==3.0.5
pip install psycopg2==2.9.6

Or, better yet, use a requirements.txt file.

flask-sqlalchemy==3.0.5
psycopg2==2.9.6

And then install the packages using the requirements.txt file.

pip install --requirement requirements.txt

app.app_context() and db.create_all() in __init__.py are used to create the Postgres database if it doesn't already exist and to be able to make session calls such as db.session.commit(). In other words, app.app_context() and db.create_all() are used to establish the connection to Postgres.

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import func, exc

db = SQLAlchemy()

def app_obj():
    app = Flask(__name__)
    uri = 'postgresql+psycopg2://johndoe:itsasecret@10.21.50.198:5432/mydb'
    app.config['SQLALCHEMY_DATABASE_URI'] = uri
    app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
    db.init_app(app)

    with app.app_context():
        try:
            db.create_all()
        except exc.SQLAlchemyError as sqlalchemyerror:
            print(sqlalchemyerror)
        except Exception as exception:
            print(exception)
        finally:
            print("no exceptions were raised")

    return app

​