Is there a way an Asset can return a warning even though it succeeds in materializing?

Yes, there is a way for an asset to return a warning even though it succeeds in materializing. This can be done by using asset checks, which are a feature in Dagster that allows you to define checks that run after an asset is materialized. You can use an

AssetCheckResult

to return a warning based on certain conditions that you define. Here's an example from the documentation that illustrates how you might implement a warning in an asset check:

python from dagster import asset, AssetCheckResult, AssetCheckSeverity  @asset def my_asset():     # ... logic to materialize the asset ...     pass  @asset_check(asset=my_asset) def my_asset_check(_):     # ... logic to determine if a warning should be issued ...     condition = True  # Replace with actual condition check     if condition:         return AssetCheckResult(             success=True,             severity=AssetCheckSeverity.WARN,             message="This is a warning message."         )

In this example,

my_asset_check

is an asset check associated with

my_asset

. If the condition within the check evaluates to

True

, it returns an

AssetCheckResult

with a warning severity, indicating that the asset materialized successfully but there is a warning message associated with it. Please note that the exact implementation and available features may vary depending on the version of Dagster you are using, so it's always a good idea to consult the latest documentation for the most up-to-date information.

@Scout how can I email this warning when it is issued?

As of my knowledge cutoff date in early 2023, Dagster does not have a built-in mechanism specifically for emailing warnings directly from asset checks. However, you can integrate Dagster with external systems to send an email when a warning is issued. This typically involves using hooks, which are functions that can be triggered by events in the Dagster lifecycle, such as the completion of an asset materialization. Here's a general approach to how you might set up an email notification for asset warnings: 1. Define a hook that sends an email. You would use an external library or service to send the email, such as

smtplib

for SMTP servers or an API client for services like SendGrid or AWS SES. 2. Attach the hook to your asset or asset check. You can use the

@success_hook

or

@failure_hook

decorators to trigger the hook based on the outcome of the asset materialization. 3. In the hook implementation, check for warnings and send an email if necessary. Here's a simplified example of how you might define and use a hook to send an email:

python
from dagster import asset, AssetCheckResult, AssetCheckSeverity, success_hook, HookContext

# Define a hook that sends an email
@success_hook(required_resource_keys={"email_client"})
def email_on_warning(context: HookContext):
    # Check if there are any warnings in the context
    for event in context.event_list:
        if event.event_type_value == "ASSET_MATERIALIZATION" and event.message:
            # Extract the warning message
            warning_message = event.message
            # Use an email client resource to send the email
            context.resources.email_client.send_email(
                subject="Dagster Asset Warning",
                body=f"Warning during asset materialization: {warning_message}",
                # Add additional email parameters as needed
            )

# Define an asset with a warning check
@asset
def my_asset():
    # ... logic to materialize the asset ...
    pass

@asset_check(asset=my_asset)
def my_asset_check(_):
    # ... logic to determine if a warning should be issued ...
    condition = True  # Replace with actual condition check
    if condition:
        return AssetCheckResult(
            success=True,
            severity=AssetCheckSeverity.WARN,
            message="This is a warning message."
        )

# Attach the hook to the asset
my_asset.with_hooks({email_on_warning})

In this example,

email_on_warning

is a hook that sends an email when it's triggered. The

email_client

is a hypothetical resource that you would need to define that handles the actual email sending logic. The

my_asset_check

function issues a warning, and the

email_on_warning

hook is attached to the

my_asset

asset using the

with_hooks

method. Please note that thi