Creating and Seeding a Database with Flask and SQLAlchemy

Flask and SQLAlchemy are two popular Python libraries that can be used to create and manage web applications. Flask is a lightweight microframework that provides a simple and flexible foundation for building web applications, while SQLAlchemy is an Object Relational Mapper (ORM) that simplifies the process of interacting with databases.

In this post, we will discuss how to create and seed a database using Flask and SQLAlchemy. It is assumed that you have a basic understanding of Python and web development.

Prerequisites

Before you begin, make sure you have the following installed on your system:

Python
Flask
SQLAlchemy

Creating a Database Schema

The first step in creating a database is to define the schema. The schema defines the structure of the database, including the tables, columns, and relationships between tables.

To define the schema, you will need to create a SQLAlchemy model for each table in your database. A SQLAlchemy model is a Python class that represents a table in the database. Each attribute of the model represents a column in the table.

For example, the following code defines a SQLAlchemy model for a User table:

from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()

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

This code defines a User model with the following attributes:

id: An integer that is the primary key of the table
name: A string that is the name of the user
email: A string that is the email address of the user

Creating a Database Connection

Once you have defined your models, you need to create a connection to the database. To do this, you will need to use the SQLAlchemy create_engine() function.

Since we are using SQLite, we will use the sqlite3 module to create the connection string:

import sqlite3

engine = create_engine('sqlite:///users.db')

This code creates a connection to a SQLite database named users.db. If the database does not exist, it will be created automatically.

Creating a Seed File

To seed the database, we will create a seed file that contains the data we want to insert. The seed file should be a Python script that imports the SQLAlchemy models and uses the db.session.add() method to insert the data into the database.

For example, the following code is a seed file that inserts two users into the database:

from app.models import User

db.session.add(User(name='John Doe', email='johndoe@example.com'))
db.session.add(User(name='Jane Doe', email='janedoe@example.com'))
db.session.commit()

Running the Seed File

To run the seed file, you can use the following command in your terminal:

python seed.py

This will execute the code in the seed file and insert the data into the database.

Conclusion

In this post, we have discussed how to create and seed a database using Flask and SQLAlchemy. We have covered the following topics:

Creating a database schema
Creating a database connection
Creating a seed file
Running the seed file

Hopefully this blog post has been helpful. If you have any questions, please leave a comment below. Thanks and good luck on your coding journey.

Resources

Flask Documentation
SQLAlchemy Documentation