Connect an SQLAlchemy application to Neon

SQLAlchemy is a Python SQL toolkit and Object Relational Mapper (ORM) that provides application developers with the full power and flexibility of SQL. This guide describes how to create a Neon project and connect to it from SQLAlchemy.

Prerequisites:

To complete the steps in this topic, ensure that you have an SQLAlchemy installation with a Postgres driver. The following instructions use psycopg2, the default driver for Postgres in SQLAlchemy. For SQLAlchemy installation instructions, refer to the SQLAlchemy Installation Guide. psycopg2 installation instructions are provided below.

To connect to Neon from SQLAlchemy:

1. Create a Neon project
2. Install psycopg2
3. Create the "hello neon" program
4. Create an SQLAlchemy engine for your Neon project

Create a Neon project

If you do not have one already, create a Neon project. Save your connection details, including your password. They are required when defining connection settings.

1. Navigate to the Projects page in the Neon Console.
2. Click New Project.
3. Specify your project settings and click Create Project.

Install psycopg2

Psycopg2 is a popular python library for running raw Postgres queries.

For most operating systems, the quickest installation method is using the PIP package manager. For example:

pip install psycopg2-binary

For additional information about installing psycopg2, refer to the psycopg2 installation documentation.

Create the "hello neon" program

import psycopg2

# Optional: tell psycopg2 to cancel the query on Ctrl-C
import psycopg2.extras; psycopg2.extensions.set_wait_callback(psycopg2.extras.wait_select)

# You can set the password to None if it is specified in a ~/.pgpass file
USERNAME = "alex"
PASSWORD = "AbC123dEf"
HOST = "@ep-cool-darkness-123456.us-east-2.aws.neon.tech"
PORT = "5432"
PROJECT = "dbname"

conn_str = f"dbname={PROJECT} user={USERNAME} password={PASSWORD} host={HOST} port={PORT} sslmode=require"

conn = psycopg2.connect(conn_str)

with conn.cursor() as cur:
 cur.execute("SELECT 'hello neon';")
 print(cur.fetchall())

You can find all of the connection details mentioned above in the Connection Details widget on the Neon Dashboard. For more information, see Connect from any application.

Create an SQLAlchemy engine for your Neon project

SQLAlchemy uses engine abstraction to manage database connections and exposes a create_engine function as the primary endpoint for engine initialization.

The following example creates an SQLAlchemy engine that points to your Neon branch:

from sqlalchemy import create_engine

USERNAME = "alex"
PASSWORD = "AbC123dEf"
HOST = "ep-cool-darkness-123456.us-east-2.aws.neon.tech"
DATABASE = "dbname"

conn_str = f'postgresql://{USERNAME}:{PASSWORD}@{HOST}/{DATABASE}?sslmode=require'

engine = create_engine(conn_str)

You can find all of the connection details listed above in the Connection Details widget on the Neon Dashboard. For more information, see Connect from any application.

For additional information about connecting from SQLAlchemy, refer to the following topics in the SQLAlchemy documentation:

• Establishing Connectivity - the Engine
• Connecting to PostgreSQL with SQLAlchemy

SQLAlchemy connection errors

• SQLAlchemy versions prior to 2.0.33 may reuse idle connections, leading to connection errors. If this occurs, you could encounter an SSL connection has been closed unexpectedly error. To resolve this, upgrade to SQLAlchemy 2.0.33 or later. For more details, see the SQLAlchemy 2.0.33 changelog.

• If you encounter an SSL SYSCALL error: EOF detected when connecting to the database, this typically happens because the application is trying to reuse a connection after the Neon compute has been suspended due to inactivity. To resolve this issue, try one of the following options:

  • Set the SQLAlchemy pool_recycle parameter to a value less than or equal to the scale to zero setting configured for your compute.
  • Set the SQLAlchemy pool_pre_ping parameter to true. This ensures that your engine checks if the connection is alive before executing a query.

  For more details on the pool_recycle and pool_pre_ping parameters, refer to SQLAlchemy: Connection Pool Configuration and Dealing with Disconnects. For information on configuring Neon's scale to zero setting, see Configuring Scale to Zero for Neon computes.

Schema migration with SQLAlchemy

For schema migration with SQLAlchemy, see our guide:

• SQLAlchemy Migrations

  Schema migration with Neon Postgres and SQLAlchemy