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#ask-ai
Title
# ask-ai
b

Binoy Shah

02/06/2024, 6:10 PM
@Scout what is the best way to add
asset_check
for a
multi_asset
s

Scout

02/06/2024, 6:10 PM
To add
asset_check
for a
multi_asset
, you can define checks within the
@multi_asset
decorator using the
check_specs
argument. Each
AssetCheckSpec
declares a check that the decorated function should yield an
AssetCheckResult
for. Here's an example from the documentation:
Copy code
python
from dagster import multi_asset, AssetOut, AssetCheckSpec, AssetCheckResult

@multi_asset(
    outs={
        "my_string_asset": AssetOut(),
        "my_int_asset": AssetOut(),
    },
    check_specs=[
        AssetCheckSpec("my_check", asset="my_string_asset"),
    ]
)
def my_function():
    # Your logic to compute the assets goes here
    my_string = "abc"
    my_int = 123

    # Perform your checks here
    check_passed = my_string == "abc"  # Replace with your actual check logic

    # Yield the AssetCheckResult for the check
    yield AssetCheckResult(
        check_name="my_check",
        asset_key="my_string_asset",
        success=check_passed,
    )

    # Return the asset values
    return my_string, my_int
In this example,
my_function
is responsible for computing the contents of the assets and performing the checks. The
check_specs
argument is used to define the checks associated with the assets. The function yields an
AssetCheckResult
for each check, indicating whether the check passed or failed, and then returns the asset values. Remember that the
asset
parameter in
AssetCheckSpec
should match the key of the asset you want to associate the check with. If you have multiple checks, you can extend the
check_specs
list with additional
AssetCheckSpec
instances for each check you want to define. Keep in mind that the example provided is a basic illustration, and you should adapt the check logic to suit your specific use case. Asset Checks on DBT Assets button Thank you for your feedback!
b

Binoy Shah

02/06/2024, 6:13 PM
@Scout and how do I add asset checks for assets that are already existing, but I cannot modify the code of the asset, for example, i have a Asset factory function that generates
@multi_asset
s

Scout

02/06/2024, 6:13 PM
If you have an existing
@multi_asset
that was created by a factory function and you cannot modify the original code, you can still add asset checks by using the
@asset_check
decorator to define separate check functions that target the assets you want to check. Here's how you can do it: 1. Define an
@asset_check
for each asset you want to check. The
@asset_check
decorator allows you to specify the asset key that the check should be associated with. 2. Implement the check logic within the decorated function, and return an
AssetCheckResult
indicating the outcome of the check. Here's an example of how you might define separate asset checks for existing assets:
Copy code
python
from dagster import asset_check, AssetCheckResult

# Assuming you have an existing asset with the key "existing_asset_key"
existing_asset_key = "existing_asset_key"

@asset_check(asset_key=existing_asset_key)
def my_asset_check(context, data):
    # Implement your check logic here
    check_passed = some_check_function(data)
    
    # Return the result of the check
    return AssetCheckResult(
        check_name="my_asset_check",
        asset_key=existing_asset_key,
        success=check_passed,
        metadata={"details": "Additional information about the check"}
    )
In this example,
some_check_function
represents the logic of your check, which you would replace with your actual validation code. The
data
parameter is the data of the asset being checked, and
context
provides access to Dagster's execution context. By using the
@asset_check
decorator, you can define checks for existing assets without modifying the original asset code. These checks will be run whenever the asset is materialized, and the results will be available in the asset catalog. Remember to replace
"existing_asset_key"
with the actual key of the asset you want to check, and implement the appropriate check logic for your use case. Forgetting asset checks on Definitions button Thank you for your feedback!
b

Binoy Shah

02/06/2024, 6:15 PM
@Scout can I have multiple asset checks for the same asset? and if yes, Does it have to be individual function for each check ?
s

Scout

02/06/2024, 6:15 PM
Yes, you can have multiple asset checks for the same asset. Each check can be defined as an individual function using the
@asset_check
decorator, and you can associate each of these functions with the same asset by specifying the asset's key. Here's an example of how you might define multiple checks for the same asset:
Copy code
python
from dagster import asset_check, AssetCheckResult

# Assuming you have an existing asset with the key "existing_asset_key"
existing_asset_key = "existing_asset_key"

@asset_check(asset_key=existing_asset_key)
def check_one(context, data):
    # Implement the first check logic here
    check_passed = check_one_logic(data)
    return AssetCheckResult(
        check_name="check_one",
        asset_key=existing_asset_key,
        success=check_passed,
        metadata={"details": "Additional information about check one"}
    )

@asset_check(asset_key=existing_asset_key)
def check_two(context, data):
    # Implement the second check logic here
    check_passed = check_two_logic(data)
    return AssetCheckResult(
        check_name="check_two",
        asset_key=existing_asset_key,
        success=check_passed,
        metadata={"details": "Additional information about check two"}
    )

# ... and so on for additional checks
In this example,
check_one_logic
and
check_two_logic
represent the logic for two separate checks. Each function is decorated with
@asset_check
and specifies the same
asset_key
, indicating that they apply to the same asset. Each check function must return an
AssetCheckResult
object, which contains the outcome of the check and any relevant metadata. By defining multiple functions, you can create a suite of checks that will all be run against the specified asset, and the results of these checks will be tracked independently in the asset catalog. This allows you to modularize your check logic and maintain clear separation between different validation rules for the same asset. Enable checks to depend on secondary ass... button Thank you for your feedback!
b

Binoy Shah

02/06/2024, 6:17 PM
@Scout Can I have only one function to make multiple checks for a single asset and return multiple check outcomes ?
s

Scout

02/06/2024, 6:17 PM
As of my knowledge cutoff date in early 2023, you cannot directly return multiple
AssetCheckResult
objects from a single
@asset_check
function. The
@asset_check
decorator is designed to create a one-to-one mapping between a check function and an asset, meaning that each check function is intended to return a single
AssetCheckResult
for the asset it is associated with. However, there is a feature request in the Dagster GitHub issues that discusses the need for multiple asset checks that execute in a single operation, which suggests that this capability might be considered for future implementation. The tracking issue is [#18068](https://github.com/dagster-io/dagster/issues/18068). If you need to perform multiple checks within a single function, you would typically define these checks within an
@op
or
@multi_asset
and yield multiple
AssetCheckResult
objects, one for each check. Here's an example using `@multi_asset`:
Copy code
python
from dagster import multi_asset, AssetOut, AssetCheckSpec, AssetCheckResult

@multi_asset(
    outs={"my_asset": AssetOut()},
    check_specs=[
        AssetCheckSpec("check_one", asset="my_asset"),
        AssetCheckSpec("check_two", asset="my_asset"),
    ]
)
def my_asset_computation():
    # Your logic to compute the asset goes here
    asset_data = compute_asset_data()

    # Perform your checks here
    check_one_passed = check_one_logic(asset_data)
    check_two_passed = check_two_logic(asset_data)

    # Yield the AssetCheckResult for each check
    yield AssetCheckResult(
        check_name="check_one",
        asset_key="my_asset",
        success=check_one_passed,
    )
    yield AssetCheckResult(
        check_name="check_two",
        asset_key="my_asset",
        success=check_two_passed,
    )

    # Return the asset value
    return asset_data
In this example,
check_one_logic
and
check_two_logic
are functions that contain the logic for two different checks. The
my_asset_computation
function yields an
AssetCheckResult
for each check. Please note that the ability to yield multiple
AssetCheckResult
objects from a single function is subject to the capabilities of the Dagster version you are using and any updates that may have occurred after my knowledge cutoff date. Always refer to the latest Dagster documentation or check the GitHub repository for the most current information and features. RFC: Asset checks button Multi-Assets | Dagster button Thank you for your feedback!
b

Binoy Shah

02/06/2024, 6:29 PM
@Scout So within a
multi_asset
is it possible to return an
Output
as well as
AssetCheckResult
?
s

Scout

02/06/2024, 6:29 PM
As of my knowledge cutoff date, within a
multi_asset
, you can yield both
Output
objects and
AssetCheckResult
objects. The
Output
objects correspond to the assets being materialized, while the
AssetCheckResult
objects correspond to checks performed on those assets. Here's an example of how you might use
multi_asset
to yield both
Output
and `AssetCheckResult`:
Copy code
python
from dagster import multi_asset, AssetOut, Output, AssetCheckResult

@multi_asset(
    outs={
        "my_asset": AssetOut(),
        # Define other assets if needed
    },
    check_specs=[
        AssetCheckSpec("my_check", asset="my_asset"),
        # Define other checks if needed
    ]
)
def my_asset_computation():
    # Your logic to compute the asset goes here
    asset_data = compute_asset_data()

    # Yield the asset data as an Output
    yield Output(asset_data, "my_asset")

    # Perform your check here
    check_passed = perform_check(asset_data)

    # Yield the AssetCheckResult for the check
    yield AssetCheckResult(
        check_name="my_check",
        asset_key="my_asset",
        success=check_passed,
    )

    # If you have other assets and checks, you would continue to yield their corresponding Outputs and AssetCheckResults
In this example,
compute_asset_data
is a placeholder for the logic that computes the data for the asset, and
perform_check
is a placeholder for the logic that performs the check on the asset data. The function yields an
Output
for the asset and an
AssetCheckResult
for the check. Please note that the ability to yield multiple results, including
Output
and
AssetCheckResult
objects, from a
multi_asset
function is subject to the capabilities of the Dagster version you are using. Always refer to the latest Dagster documentation or check the GitHub repository for the most current information and features. add key_prefix to multi_asset button Graph-Backed Assets | Dagster button Thank you for your feedback!