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

Often, the logic for the initial setup of the database is placed in __init__.py. Here is how you can determine if SQLite table exists.

• create_engine and MetaData are used to determine if the SQLite table exists
• sqlite followed by 3 forward slashes means relative path or present working directory (e.g. sqlite:///example.db). In this scenario, the example.db file would need to be in the same directory as the __init__.py file.
• sqlite followed by 4 forward slashes means full or absolute path (e.g. sqlite:////usr/local/flask/database/example.db)
• Let's say you have example.db on a network share and on your Windows PC you map a network drive resulting in something like Z:/example.db. In this scenario, you would use 3 forward slashes followed by the mapped network drive (e.g. sqlite:///Z:/example.db). This would probably only be done on your PC for local testing and development purposes.

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

db = SQLAlchemy()

def app_obj():
    app = Flask(__name__)
    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///example.db'
    app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
    db.init_app(app)

    try:
        engine = create_engine("sqlite:///example.db")
    except exc.SQLAlchemyError as sqlalchemyerror:
        print(f"got the following SQLAlchemyError: {sqlalchemyerror}")
    except Exception as exception:
        print(f"got the following Exception: {exception}")

    metadata = MetaData()
    metadata.reflect(bind=engine)
    my_table = metadata.tables['my_table']

    if my_table is None:
        print(f"my_table does not exist")
    else:
        print(f"my_table exists)

    return app