How to install SQLalchemy, then connect to managed PostgreSQL DB

Hi there,

Here’s a rough guide on how to install SQLAlchemy and connect it to a DigitalOcean Managed PostgreSQL database in a Flask application.

1. Install SQLAlchemy

First, you need to install SQLAlchemy in your Flask environment. You can do that with pip:

pip install SQLAlchemy

2. Install psycopg2-binary

SQLAlchemy uses a driver to talk with your PostgreSQL database. The most common one is psycopg2. However, compiling psycopg2 from source can be a bit of a hassle, so we’ll use psycopg2-binary, which is a stand-alone package and easy to install:

pip install psycopg2-binary

3. Create your SQLAlchemy engine

Now you can create your SQLAlchemy engine. The engine is what SQLAlchemy uses to interface with your database. Here’s an example of how you might set up the engine in your Flask app:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

# replace the user, password, host and dbname with your actual credentials
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://user:password@host:port/dbname?sslmode=require&sslrootcert=/path/to/ca-certificate.crt'

db = SQLAlchemy(app)

In this connection string, sslmode=require tells PostgreSQL to use SSL, and sslrootcert is used to specify the path to the CA certificate file. Replace /path/to/ca-certificate.crt with the actual path to your certificate file. This should allow you to connect to your DigitalOcean Managed PostgreSQL database using SQLAlchemy with SSL.

4. Define your database models

Now you can define your database models. Here’s an example of a simple User model:

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50), nullable=False)

5. Create your database tables

With your models defined, you can create the tables in your database:

db.create_all()

You usually only want to run this once, when you first set up your application.

6. Pulling data from DB and displaying it via a Flask/Jinja2 template

Firstly, make sure you’ve imported your models at the top of your file:

from models import User

Then, you can query the database for users like so:

users = User.query.all()

And you can pass these users to your template:

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

And in your users.html template, you could display the users with something like this:

<ul>
{% for user in users %}
    <li>{{ user.name }}</li>
{% endfor %}
</ul>

This is a very basic example and SQLAlchemy can do much more, but hopefully, this will help you get started.

Remember to always secure your database credentials. Do not hardcode them in your application. Consider using environment variables or secure secrets management systems.

Also, keep in mind that SQLAlchemy provides a Pythonic way to interact with your database. You’ll still need to understand SQL and your database system to make effective use of it.

For more detailed information, I recommend checking out the SQLAlchemy documentation.

Best,

Bobby