How to use Flask-SQLAlchemy for database operations

How to use Flask-SQLAlchemy for database operations

Flask-SQLAlchemy is a convenient extension that can operate databases in Flask applications. It provides simple API to reduce developer workload and integrates seamlessly with the Flask framework. This article will introduce how to use Flask-SQLAlchemy for database operations and provide code examples.

1. Install Flask-SQLAlchemy
   First, you need to install the Flask-SQLAlchemy extension. It can be installed by running the following command in a command line window using the pip command:

pip install flask-sqlalchemy

2. Configuring the database connection
   Add the database connection configuration in the Flask application's configuration file. Different databases such as MySQL, SQLite, PostgreSQL etc. can be used. The following is an example configuration using a SQLite database:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

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

3. Define the model
   Using Flask-SQLAlchemy, you can define a model to map tables in the database. A model is a Python class that corresponds to a table and the columns of the table in the database. The following is the definition of an example model:

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)
    
    def __repr__(self):
        return '<User %r>' % self.username

4. Create database table
   In Flask-SQLAlchemy, you can use the db.create_all() method to create a database table. This method can be called when the application starts to ensure the correctness of the database structure. Here is an example:

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

5. Perform database operations
   With Flask-SQLAlchemy, you can easily perform database operations such as inserting, querying, updating, and deleting data. Here are some basic examples:

• Insert data:

user = User(username='John', email='john@example.com')
db.session.add(user)
db.session.commit()

• Query data:

all_users = User.query.all()

user = User.query.filter_by(username='John').first()

• Update data:

user = User.query.filter_by(username='John').first()
user.email = 'newemail@example.com'
db.session.commit()

• Delete data:

user = User.query.filter_by(username='John').first()
db.session.delete(user)
db.session.commit()

This is just the basic usage of Flask-SQLAlchemy. It also provides more advanced features such as query filtering, sorting, and paging. You can check out the official documentation of Flask-SQLAlchemy to learn more.

Summary
This article introduces how to use Flask-SQLAlchemy for database operations and provides code examples. With Flask-SQLAlchemy, database operations can be easily handled to speed up development and increase efficiency. Hope this article helps you!

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