Seventh Installation of Flask Tutorial Series: Explored Databases and SQLAlchemy

In this tutorial, we will be discussing databases and how to use SQLAlchemy with Flask. SQLAlchemy is a powerful Python library for working with databases, and it provides a high-level API for interacting with databases in a more Pythonic way. In this tutorial series, we will focus on using SQLAlchemy with Flask, a popular web framework for building web applications in Python.

Before we dive into using SQLAlchemy with Flask, let’s first understand the basics of databases. A database is an organized collection of data, typically stored and accessed electronically from a computer system. Databases can be relational or non-relational, but for this tutorial, we will be focusing on relational databases.

A relational database is a type of database that stores and provides access to data points that are related to one another. These data points are organized into tables, which consist of rows and columns. Each row in a table represents a record, and each column represents a field or an attribute of the record. In relational databases, tables can be related to one another through keys, such as primary keys and foreign keys.

Now, let’s talk about SQLAlchemy. SQLAlchemy is an Object-Relational Mapping (ORM) library for Python that provides a high-level abstraction for interacting with databases. With SQLAlchemy, you can work with databases using Python objects and methods, rather than writing SQL queries directly. SQLAlchemy supports a wide variety of database systems, including SQLite, MySQL, PostgreSQL, and more.

In this tutorial series, we will be using SQLite as our database system, as it is lightweight and easy to setup for development purposes. SQLite is a self-contained, serverless, zero-configuration database engine that is widely used in web applications for storing data locally.

To get started with using SQLAlchemy with Flask, you will first need to install the required dependencies. You can do this by running the following command:

pip install Flask SQLAlchemy

Next, let’s create a new Flask project and set up our database using SQLAlchemy. Create a new Python file, for example app.py, and add the following code:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///db.sqlite'
db = SQLAlchemy(app)

if __name__ == '__main__':
    app.run()

In this code snippet, we first import the required libraries – Flask and SQLAlchemy. We then create a new Flask app instance and configure the database URI to point to a SQLite database file called db.sqlite. Next, we create a new SQLAlchemy instance and pass in the Flask app object to bind them together.

You can now create your database models by defining Python classes that represent tables in your database. For example, let’s create a simple User model to store user information:

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(50), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)

    def __repr__(self):
        return f'<User {self.username}>'

In this User model, we defined a table with three columns – id, username, and email. The id column is the primary key, which uniquely identifies each user record. The username and email columns are defined as string fields with specific length constraints.

To create the initial database schema, you can run the following commands in a Python shell:

from app import db
db.create_all()

This will create the necessary tables in the SQLite database file db.sqlite based on the models you have defined. You can now interact with the database using SQLAlchemy methods such as db.session.add(), db.session.commit(), db.session.query(), and so on.

For example, to add a new user to the database, you can do the following:

from app import db, User

new_user = User(username='john_doe', email='john.doe@example.com')
db.session.add(new_user)
db.session.commit()

To query all users from the database, you can do the following:

from app import db, User

users = User.query.all()
for user in users:
    print(user.username, user.email)

In this tutorial series, we have covered the basics of databases, SQLAlchemy, and how to use SQLAlchemy with Flask to interact with a SQLite database. You can now expand on this knowledge by exploring more advanced features of SQLAlchemy, such as relationships between tables, queries, and more. SQLAlchemy provides a rich set of features for working with databases, and it is a powerful tool for building web applications with Flask.