I have an asset which needs to have access to external API credentials. During testing, I do not have access to these credentials, so I would like to mock this. Please show me a code snippet of how I can achieve this using resources. The example should show the asset using the API credentials in production as well as a test which materializes the asset using the mocked resource.

Certainly! To achieve this, you would define a resource that provides access to the external API credentials and then use different implementations of this resource for production and testing environments. Here's a step-by-step guide based on the documentation: 1. Define a resource that encapsulates the API client, which requires credentials. In production, this resource will use the real credentials to access the API. 2. Define a mock resource for testing that simulates the behavior of the API without requiring real credentials. 3. Create an asset that depends on this resource. The asset will use the resource to interact with the API. 4. In your tests, materialize the asset using the mocked resource to avoid the need for real credentials. Here's a code snippet that demonstrates this pattern:

python from dagster import resource, asset, Field, StringSource, build_asset_context  # Define a resource for the production API client @resource({     "api_key": Field(StringSource, description="API key for the external API") }) def api_client_resource(context):     api_key = context.resource_config["api_key"]     # Replace 'ExternalAPIClient' with your actual client class     return ExternalAPIClient(api_key)  # Define a mock resource for testing @resource def mock_api_client_resource(_):     # Replace 'MockExternalAPIClient' with your mock client class     return MockExternalAPIClient()  # Define an asset that uses the API client resource @asset(required_resource_keys={"api_client"}) def my_asset(context):     api_client = context.resources.api_client     # Use the API client to interact with the external API     data = api_client.get_data()     return data  # Example test that materializes the asset using the mocked resource def test_my_asset():     with build_asset_context(resources={"api_client": mock_api_client_resource}) as context:         result = my_asset(context=context)         # Perform assertions on 'result'

In this example,

ExternalAPIClient

would be a class that interacts with the real external API, and

MockExternalAPIClient

would be a class that simulates the API for testing purposes. The

api_client_resource

function creates an instance of the real API client using the provided API key, while

mock_api_client_resource

creates an instance of the mock client. When running tests, you use

build_asset_context

to provide the

mock_api_client_resource

to the asset, which allows you to test the asset's logic without needing real API credentials. Please note that the actual implementation of

ExternalAPIClient

and

MockExternalAPIClient

will depend on the specifics of the external API you're interacting with and how you want to simulate it for testing.

@Scout please update the provided example by using the pydantic resource definition instead of the legacy resource approach.

Certainly! With the introduction of Pythonic resources in Dagster, you can define resources using Pydantic models. Here's how you can update the example to use Pydantic resources: First, you'll need to define a Pydantic model for your resource configuration:

python from pydantic import BaseModel from dagster import asset, build_asset_context from dagster_pydantic import PydanticConfigurableResource  # Define a Pydantic model for the API client configuration class APIClientConfig(BaseModel):     api_key: str  # Define a resource for the production API client using the Pydantic model class APIClientResource(PydanticConfigurableResource[APIClientConfig]):     def __init__(self, config: APIClientConfig):         # Replace 'ExternalAPIClient' with your actual client class         self.client = ExternalAPIClient(config.api_key)  # Define a mock resource for testing class MockAPIClientResource(PydanticConfigurableResource):     def __init__(self):         # Replace 'MockExternalAPIClient' with your mock client class         self.client = MockExternalAPIClient()  # Define an asset that uses the API client resource @asset(required_resource_keys={"api_client"}) def my_asset(context):     api_client = context.resources.api_client.client     # Use the API client to interact with the external API     data = api_client.get_data()     return data  # Example test that materializes the asset using the mocked resource def test_my_asset():     with build_asset_context(resources={"api_client": MockAPIClientResource()}) as context:         result = my_asset(context=context)         # Perform assertions on 'result'

In this updated example,

APIClientConfig

is a Pydantic model that defines the configuration schema for the API client resource.

APIClientResource

and

MockAPIClientResource

are resource classes that inherit from

PydanticConfigurableResource

, with

APIClientResource

taking an instance of

APIClientConfig

as its configuration. When you materialize the asset in your tests, you instantiate

MockAPIClientResource

directly without any configuration, since it's a mock that doesn't require real credentials. Please ensure that you have the

dagster_pydantic

package installed to use

PydanticConfigurableResource

. If it's not already installed, you can add it to your project with

pip install dagster_pydantic

. Remember to replace

ExternalAPIClient

and

MockExternalAPIClient

with the actual implementations that correspond to your production and mock API clients, respectively.