How Can We Request Database Connections in Flask?

In Flask, database connections can be requested and managed using the Flask-SQLAlchemy extension, which is built on top of the popular SQLAlchemy library.

Here are the basic steps to request database connections in Flask using Flask-SQLAlchemy:

1. Install Flask-SQLAlchemy: You can install Flask-SQLAlchemy using pip, by running the following command:

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!pip install flask_sqlalchemy

1. Configure the database: In your Flask app, you need to configure the database connection details, such as the database URL, username, and password. You can do this by setting the SQLALCHEMY_DATABASE_URI configuration option in your Flask app's configuration. For example:

app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://user:password@localhost/mydatabase'

This example sets the database URL for a PostgreSQL database running on the local machine with the username 'user', password 'password', and the database name 'mydatabase'.

1. Create a SQLAlchemy object: In your Flask app, you need to create a SQLAlchemy object, which will handle the database connections and queries. You can do this by creating an instance of the SQLAlchemy class, and passing your Flask app as an argument. For example:

In [ ]:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://user:password@localhost/mydatabase'

db = SQLAlchemy(app)

1. Request a database connection: You can request a database connection by using the db.session object, which is a session that handles the database connection. For example, to query the database, you can do the following:

In [ ]:

from models import User

@app.route('/users')
def list_users():
    users = User.query.all()
    return render_template('users.html', users=users)

In this example, we are using the query method of the User model to fetch all the users from the database.

That's the basic process for requesting database connections in Flask using Flask-SQLAlchemy. With this setup, Flask will automatically handle the opening and closing of database connections, so you don't need to worry about managing the connections yourself.