Making a Flask app using a PostgreSQL database (original) (raw)

Last Updated : 26 Apr, 2025

The Postgres database can be accessed via one of two methods in Python. Installing PgAdmin4 is the first step because it offers a user interface for interacting with databases and another for using the psycopg2 connector. In this post, we'll concentrate on a different approach that lets us alter the Postgres database: using the psycopg2 connector. This article presupposes that Postgres has been successfully installed on your computer or device.

Let's get started on the project. An HTML page will be added to display the modifications, along with a few products and their prices. It will include the three tables. earliest for product details. second to update existing items, and third to add new ones.

Steps to make Flask app using a PostgreSQL Database

Step 1: Open your command line tool and connect with Postgres. After entering the username it will ask you for the password enter it appropriately.

psql -U username

Step 2: Once we successfully connected then create a new database 'flask_db'. We will use it further to create tables in it.

Making a Flask app using a PostgreSQL database

Step 3: Create a folder structure like this.

Step 4: Connect with the database. you will have to use psycopg2 connect to use the commands.

Python3 `

conn = psycopg2.connect(database="flask_db", user="postgres", password="root", host="localhost", port="5432")

cur = conn.cursor()

conn.commit()

cur.close() conn.close()

Step 5: app.py

This will authenticate the user and allows us to execute queries on it. It creates a cursor on the connection by using cur. execute() method executes the queries for us. Once we completed our queries we have to close the connection for security purposes.

Python3 `

from flask import Flask, render_template, request, redirect, url_for import psycopg2

app = Flask(name)

Connect to the database

conn = psycopg2.connect(database="flask_db", user="postgres", password="root", host="localhost", port="5432")

create a cursor

cur = conn.cursor()

if you already have any table or not id doesnt matter this

will create a products table for you.

cur.execute( '''CREATE TABLE IF NOT EXISTS products (id serial
PRIMARY KEY, name varchar(100), price float);''')

Insert some data into the table

cur.execute( '''INSERT INTO products (name, price) VALUES
('Apple', 1.99), ('Orange', 0.99), ('Banana', 0.59);''')

commit the changes

conn.commit()

close the cursor and connection

cur.close() conn.close()

@app.route('/') def index(): # Connect to the database conn = psycopg2.connect(database="flask_db", user="postgres", password="root", host="localhost", port="5432")

# create a cursor
cur = conn.cursor()

# Select all products from the table
cur.execute('''SELECT * FROM products''')

# Fetch the data
data = cur.fetchall()

# close the cursor and connection
cur.close()
conn.close()

return render_template('index.html', data=data)

@app.route('/create', methods=['POST']) def create(): conn = psycopg2.connect(database="flask_db", user="postgres", password="root", host="localhost", port="5432")

cur = conn.cursor()

# Get the data from the form
name = request.form['name']
price = request.form['price']

# Insert the data into the table
cur.execute(
    '''INSERT INTO products \
    (name, price) VALUES (%s, %s)''',
    (name, price))

# commit the changes
conn.commit()

# close the cursor and connection
cur.close()
conn.close()

return redirect(url_for('index'))

@app.route('/update', methods=['POST']) def update(): conn = psycopg2.connect(database="flask_db", user="postgres", password="root", host="localhost", port="5432")

cur = conn.cursor()

# Get the data from the form
name = request.form['name']
price = request.form['price']
id = request.form['id']

# Update the data in the table
cur.execute(
    '''UPDATE products SET name=%s,\
    price=%s WHERE id=%s''', (name, price, id))

# commit the changes
conn.commit()
return redirect(url_for('index'))

@app.route('/delete', methods=['POST']) def delete(): conn = psycopg2.connect (database="flask_db", user="postgres", password="root", host="localhost", port="5432") cur = conn.cursor()

# Get the data from the form
id = request.form['id']

# Delete the data from the table
cur.execute('''DELETE FROM products WHERE id=%s''', (id,))

# commit the changes
conn.commit()

# close the cursor and connection
cur.close()
conn.close()

return redirect(url_for('index'))

if name == 'main': app.run(debug=True)

You will need this index file to see results and perform operations. Just add these template codes to their respective path.