prefect-sqlalchemy

The prefect-sqlalchemy collection makes it easy to connect to a database in your Prefect flows. Check out the examples below to get started!

Getting started

Integrate with Prefect flows

Prefect and SQLAlchemy are a data powerhouse duo. With Prefect, your workflows are orchestratable and observable, and with SQLAlchemy, your databases are a snap to handle! Get ready to experience the ultimate data "flow-chemistry"!

To set up a table, use the execute and execute_many methods. Then, use the fetch_many method to retrieve data in a stream until there's no more data.

By using the SqlAlchemyConnector as a context manager, you can make sure that the SQLAlchemy engine and any connected resources are closed properly after you're done with them.

Be sure to install prefect-sqlalchemy and save your credentials to a Prefect block to run the examples below!

Async support

SqlAlchemyConnector also supports async workflows! Just be sure to save, load, and use an async driver as in the example below.

from prefect_sqlalchemy import SqlAlchemyConnector, ConnectionComponents, AsyncDriver

connector = SqlAlchemyConnector(
    connection_info=ConnectionComponents(
        driver=AsyncDriver.SQLITE_AIOSQLITE,
        database="DATABASE-PLACEHOLDER.db"
    )
)

connector.save("BLOCK_NAME-PLACEHOLDER")

SyncAsync

from prefect import flow, task
from prefect_sqlalchemy import SqlAlchemyConnector


@task
def setup_table(block_name: str) -> None:
    with SqlAlchemyConnector.load(block_name) as connector:
        connector.execute(
            "CREATE TABLE IF NOT EXISTS customers (name varchar, address varchar);"
        )
        connector.execute(
            "INSERT INTO customers (name, address) VALUES (:name, :address);",
            parameters={"name": "Marvin", "address": "Highway 42"},
        )
        connector.execute_many(
            "INSERT INTO customers (name, address) VALUES (:name, :address);",
            seq_of_parameters=[
                {"name": "Ford", "address": "Highway 42"},
                {"name": "Unknown", "address": "Highway 42"},
            ],
        )

@task
def fetch_data(block_name: str) -> list:
    all_rows = []
    with SqlAlchemyConnector.load(block_name) as connector:
        while True:
            # Repeated fetch* calls using the same operation will
            # skip re-executing and instead return the next set of results
            new_rows = connector.fetch_many("SELECT * FROM customers", size=2)
            if len(new_rows) == 0:
                break
            all_rows.append(new_rows)
    return all_rows

@flow
def sqlalchemy_flow(block_name: str) -> list:
    setup_table(block_name)
    all_rows = fetch_data(block_name)
    return all_rows


sqlalchemy_flow("BLOCK-NAME-PLACEHOLDER")

from prefect import flow, task
from prefect_sqlalchemy import SqlAlchemyConnector
import asyncio

@task
async def setup_table(block_name: str) -> None:
    async with await SqlAlchemyConnector.load(block_name) as connector:
        await connector.execute(
            "CREATE TABLE IF NOT EXISTS customers (name varchar, address varchar);"
        )
        await connector.execute(
            "INSERT INTO customers (name, address) VALUES (:name, :address);",
            parameters={"name": "Marvin", "address": "Highway 42"},
        )
        await connector.execute_many(
            "INSERT INTO customers (name, address) VALUES (:name, :address);",
            seq_of_parameters=[
                {"name": "Ford", "address": "Highway 42"},
                {"name": "Unknown", "address": "Highway 42"},
            ],
        )

@task
async def fetch_data(block_name: str) -> list:
    all_rows = []
    async with await SqlAlchemyConnector.load(block_name) as connector:
        while True:
            # Repeated fetch* calls using the same operation will
            # skip re-executing and instead return the next set of results
            new_rows = await connector.fetch_many("SELECT * FROM customers", size=2)
            if len(new_rows) == 0:
                break
            all_rows.append(new_rows)
    return all_rows

@flow
async def sqlalchemy_flow(block_name: str) -> list:
    await setup_table(block_name)
    all_rows = await fetch_data(block_name)
    return all_rows


asyncio.run(sqlalchemy_flow("BLOCK-NAME-PLACEHOLDER"))

Resources

For more tips on how to use tasks and flows provided in a Prefect integration library, check out the Prefect docs on using integrations.

Install prefect-sqlalchemy for Prefect 2

pip install 'prefect[sqlalchemy]<3'

We recommend using a Python virtual environment manager such as pipenv, conda, or virtualenv.

The tasks in this library are designed to work with Prefect 2. For more information about how to use Prefect, please refer to the Prefect documentation.

Saving credentials to a block

To use the load method on Blocks, you must have a block document saved through code or saved through the UI.

Below is a walkthrough on saving block documents through code; simply create a short script, replacing the placeholders.

from prefect_sqlalchemy import SqlAlchemyConnector, ConnectionComponents, SyncDriver

connector = SqlAlchemyConnector(
    connection_info=ConnectionComponents(
        driver=SyncDriver.POSTGRESQL_PSYCOPG2,
        username="USERNAME-PLACEHOLDER",
        password="PASSWORD-PLACEHOLDER",
        host="localhost",
        port=5432,
        database="DATABASE-PLACEHOLDER",
    )
)

connector.save("BLOCK_NAME-PLACEHOLDER")

Congrats! You can now easily load the saved block, which holds your credentials:

from prefect_sqlalchemy import SqlAlchemyConnector

SqlAlchemyConnector.load("BLOCK_NAME-PLACEHOLDER")

The required keywords depend upon the desired driver. For example, SQLite requires only the driver and database arguments:

from prefect_sqlalchemy import SqlAlchemyConnector, ConnectionComponents, SyncDriver

connector = SqlAlchemyConnector(
    connection_info=ConnectionComponents(
        driver=SyncDriver.SQLITE_PYSQLITE,
        database="DATABASE-PLACEHOLDER.db"
    )
)

connector.save("BLOCK_NAME-PLACEHOLDER")

Registering blocks

Register blocks in this module to view and edit them on Prefect Cloud:

prefect block register -m prefect_sqlalchemy

Feedback

If you encounter any bugs while using prefect-sqlalchemy, please open an issue in the prefect repository.

If you have any questions or issues while using prefect-sqlalchemy, you can find help in the Prefect Community Slack.

Contributing

If you'd like to help contribute to fix an issue or add a feature to prefect-sqlalchemy, please propose changes through a pull request from a fork of the repository.

Here are the steps:

1. Fork the repository
2. Clone the forked repository
3. Install the repository and its dependencies:

pip install -e ".[dev]"

1. Make desired changes
2. Add tests
3. Install pre-commit to perform quality checks prior to commit:

pre-commit install

1. git commit, git push, and create a pull request