Catalogs

A catalog is collection of IOs. From experience, we find that separating these IO from transformations (nodes) keeps your code clean and maintainable. Catalogs help you organize and swap IOs across different environments — such as local development, production, or testing — without changing your nodes. This makes it easy to run the same pipeline with different data sources or destinations.

Defining catalogs

To create a catalog, make a Python module where each IO is a variable. For example, a local catalog might look like this:

catalogs/local.py

from ordeq_spark import SparkCSV

iris = SparkCSV(path="path/to/local/iris.csv")
predictions = SparkCSV(path="path/to/local/predictions.csv")

Here, iris and predictions are IOs pointing to local CSV files.

IO naming convention

Following PEP-8, IO instances should be lowercased. For instance, use iris instead of Iris. IO classes, on the other hand, should be in PascalCase, such as SparkCSV.

For production, you might want to use different IOs, such as tables in a data lake:

catalogs/production.py

from ordeq_spark import SparkIcebergTable

iris = SparkIcebergTable(table="iris")
predictions = SparkIcebergTable(table="predictions")

Notice that both catalogs use the same variable names (iris, predictions), but the IOs themselves are different: one uses CSV files, the other uses Iceberg tables.

Now you can use the IOs in your nodes by importing the catalog:

nodes.py

from ordeq import node
from pyspark.sql import DataFrame

from catalogs import local  # or 'production'


@node(inputs=local.iris, outputs=local.predictions)
def predict(iris: DataFrame) -> DataFrame:
    # Your prediction logic here
    ...

Avoid individual IO imports

It is best practice to import the catalog entirely, rather than individual IOs. This keeps the import statements clean, and makes it easier to switch catalogs. It also avoids name clashes between IOs and function arguments in your code.

Switching between catalogs

You can select which catalog to use based on the environment that your code runs in. An easy way to do this is by using an environment variable. Say you want to switch between the local and production catalogs based on an environment variable called ENV. You can do so as follows:

catalogs/__init__.py

import os
from catalogs import local, production

catalog = local if os.getenv("ENV") == "local" else production

Now, you can use the resolved catalog in your nodes:

nodes.py

from ordeq import node
from pyspark.sql import DataFrame

from catalogs import catalog  # resolves to 'local' or 'production'


@node(inputs=catalog.iris, outputs=catalog.predictions)
def predict(iris: DataFrame) -> DataFrame:
    # Your prediction logic here
    ...

When the environment variable ENV=local it uses the local catalog. For any other value, it uses the production catalog.

Ensuring consistency

It is important that all your catalogs define the same IOs (that is, the same variable names). This prevents errors when switching between environments.

You can check catalog consistency using the check_catalogs_are_consistent function. Here is how you would adapt the previous script:

catalogs/__init__.py

import os
from ordeq import check_catalogs_are_consistent

from catalogs import local, production

check_catalogs_are_consistent(local, production)
catalog = local if os.getenv("ENV") == "local" else production

If the catalogs have different variable names, this function will raise an error, helping you catch mistakes early.

When (not) to use catalogs

Creating separate modules for different environments makes most sense if each module contains a different set of IOs that cannot be otherwise resolved at run-time.

For instance, if the only difference between your local and production environments is the namespace, you can use environment variables or configuration file to set the table names dynamically, rather than creating separate catalogs:

catalog.py

from ordeq_spark import SparkCSV

ns = os.getenv("NAMESPACE", "default")
iris = SparkIcebergTable(table=f"{ns}.iris")
predictions = SparkIcebergTable(table=f"{ns}.predictions")

This approach is simpler and avoids the overhaead of multiple catalog modules.

Extending catalogs

Often we do not want to create a new catalog from scratch, but rather extend an existing one. For example, you might want to create a staging catalog that is similar to production, but with a few differences. You can do this by importing the base catalog and overriding specific IOs:

catalogs/staging.py

from ordeq_spark import SparkCSV

from catalogs.production import *

iris = SparkCSV(path="path/to/staging/iris.csv")  # Override iris IO

This way, the staging catalog inherits all IOs from production, except for iris, which is replaced with a CSV.

You can also extend catalogs, as follows:

catalogs/staging.py

from ordeq_spark import SparkCSV

from catalogs.production import *

iris_large = SparkCSV(
    path="path/to/staging/iris_large.csv"
)  # Extends with a new IO

Note that the extended catalog is not consistent with the production catalog, since it defines a new IO.

Using catalogs in tests

Catalogs are useful for testing, because you can easily swap to test IOs. First, define a test catalog with test IOs:

from ordeq_spark import SparkCSV

iris = SparkCSV(path="path/to/test/iris.csv")
predictions = SparkCSV(path="path/to/test/predictions.csv")

You can place the catalog in the source package, with the other catalogs. In that case, you can import it in your nodes as shown above.

If you place the catalog in another package, say the tests package, the easiest way to use the test catalog is to patch:

test_nodes.py

from ordeq import run
from unittest import patch

import nodes
import tests


@patch("nodes.catalog", new=tests.catalog)
def test_it_predicts(catalog):
    actual = run(predict)
    assert predictions.load() == ...  # do your assertions here

Limitation

Patching a catalog only works if the catalog is a plain module, not a package.

If you do not want to create a new catalog, you can run nodes with alternative IOs directly:

test_nodes.py

from ordeq import run
from ordeq_spark import SparkCSV

from catalogs import catalog


def test_it_predicts():
    actual = run(predict, io={catalog.iris: SparkCSV(path="path/to/test.csv")})
    assert catalog.predictions.load() == ...  # do your assertions here

This is especially useful for unit tests. Checkout the node testing guide for more details.