Flask Tutorial for 2023

This was my flask tutorial to resolve app-context issues that were preventing me from completing the flask tutorial by 'Tech with Tim' that spanned more than ten bite sized videos. When I got to tutorial 8 I could not get the sqlite database to work try as I may even after changing my code to accomodate the suggestions in stack overflow website. I next tried the tutorial inside the flask-sqlalchemy site. That did not work either. Finally I had no choice but to leverage a previous package I build that worked that was for the usage of blueprints in flask. I am still curious to know what went wrong but for now this repo documents how with limited modularity I was able to get my sqlite database to work.

Choose python version and setup virtual environment

I chose python3 version 3.9.2. I use pyenv to manage my python versions. I use virtualenv as it allows me to make a directory local to a virtual environment so that I don't need to remember to activate the environment when working inside. However since I use VS Code I still need to setup the correct virtual environment to match my command line interface.

% pyenv 3.9.2 virtualenv flask-tutorial
% pyenv local flask-tutorial
% pyenv activate flask-tutorial

The last command is needed when virtualenv is buggy and needs prompting!

Install Flask and flask_sqlalchemy

Install the packages inside the command line interface.

% pip install flask
% pip install flask-sqlalchemy

Alternatively we can add them to a requirements.txt file and run the file. This keeps the file free of clutter as the sub-packages are not included. So type the following inside your requirments.txt file.

Flask==2.3.2
Flask-SQLAlchemy==3.0.3

The above was done using the below commands and trimming out the extra packages that are not required when using github.

% pip freeze > requirements.txt

create a folder for your package

In this example I create a folder 'server' and added a file init.py inside to make it a python package. This file has most of my code, including my models and views. In another tutorial on Blueprints, these are parcelled into different directories for tidiness and ease of sharing as an application. The code you see inside reflects my efforts to work through the flask-sqlalchemy tutorial found here in this link.

Add init.py to your package

% touch __init__.py

Import Flask, SQLAlchemy into init.py

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

Add instance of SQLAlchemy

db = SQLAlchemy()

Add method 'create_app' & instance of Flask

def create_app():
    app = Flask(__name__)

Generate a secret key and add to 'app' the Flask app

Generate your secret key using your python prompt.

% python
>>> import secrets
>>> print(secrets.token_hex())
34ed0ded2daa847961058c04ab88b4069a6155cb771094e22d32d7aaed01c333

def create_app():
    app = Flask(__name__)
    app.secret_key = '34ed0ded2daa847961058c04ab88b4069a6155cb771094e22d32d7aaed01c333'

Config the path to the database of choice

app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///project.db"

Initiatize the database using the Flask app

db.init_app(app)

Add tables using models or classes

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String, unique=True, nullable=False)
    email = db.Column(db.String)

    def __init__(self, username, email):
        self.username = username
        self.email = email

Add views

        @app.route("/users")
        def user_list():
            users = db.session.execute(db.select(User).order_by(User.username)).scalars()
            return render_template("user/list.html", users=users)

        @app.route("/users/create", methods=["GET", "POST"])
        def user_create():
            if request.method == "POST":
                user = User(
                    username=request.form["username"],
                    email=request.form["email"],
                )
                db.session.add(user)
                db.session.commit()
                return redirect(url_for("user_detail", id=user.id))

            return render_template("user/create.html")

        @app.route("/user/<int:id>")
        def user_detail(id):
            user = db.get_or_404(User, id)
            print(user.username, user.email)
            return render_template("user/detail.html", user=user)

        @app.route("/user/<int:id>/delete", methods=["GET", "POST"])
        def user_delete(id):
            user = db.get_or_404(User, id)

            if request.method == "POST":
                db.session.delete(user)
                db.session.commit()
                return redirect(url_for("user_list"))

            return render_template("user/delete.html", user=user)

Once models are defined and imported add context

with app.app_context():
    db.create_all()

return app

Add a main python file to import and call the 'create_app'

from server import create_app

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

Add the html files to the templates directory

Add as required.