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Title
# ask-ai
t

Tobias Macey

02/13/2024, 8:15 PM
How can I attach a dynamically partitioned asset sensor to an op for processing external assets?
s

Scout

02/13/2024, 8:15 PM
To attach a dynamically partitioned asset sensor to an op for processing external assets, you would typically define a sensor that monitors the external asset and triggers a job or op when a new partition is detected. However, the documentation does not provide a direct example of attaching a dynamically partitioned asset sensor to an op. It does provide information on how to work with external assets and sensors in general. Here's a high-level approach based on the concepts from the documentation: 1. Define the External Asset: You would first declare your external asset using
AssetSpec
and
external_assets_from_specs
if you're dealing with an asset that is not materialized by Dagster but you want to track it within Dagster's asset catalog. 2. Create a Sensor: You would then define a sensor using the
@sensor
decorator. This sensor would be responsible for checking the external system for new partitions of the asset and triggering a run when it detects changes. 3. Trigger a Job or Op: When the sensor detects a new partition, it should trigger a job or op that processes the new partition. This can be done by returning a
RunRequest
from the sensor function, which includes the necessary run configuration for the job or op that processes the asset. 4. Use the Python API: If you need to backfill metadata or report events for the external asset, you can use the
report_runless_asset_event
method on the
DagsterInstance
to insert events directly from Dagster's Python API. Here is a simplified example based on the documentation's guidance:
Copy code
python
from dagster import sensor, RunRequest, DagsterInstance, AssetMaterialization

# Assume 'my_external_asset_op' is an op that processes the external asset
from my_project import my_external_asset_op

@sensor(job=my_external_asset_op)
def my_external_asset_sensor(context):
    # Logic to check for new partitions in the external system
    new_partitions = check_for_new_partitions()

    if new_partitions:
        for partition in new_partitions:
            # Trigger a run for each new partition
            yield RunRequest(
                run_key=partition,  # Unique identifier for the run
                run_config={
                    # Include necessary run configuration for processing the partition
                },
            )

# Function to check for new partitions in the external system
def check_for_new_partitions():
    # Implement logic to detect new partitions
    pass

# Assuming you have a DagsterInstance
instance = DagsterInstance.get()

# Report an asset event without a run
instance.report_runless_asset_event(
    AssetMaterialization(
        "external_asset_partition", metadata={"partition": "new_partition"}
    )
)
Please note that this is a high-level exa
mple and the actual implementation details would depend on your specific use case, such as how you detect new partitions and how your ops are defined to process them. The documentation does not provide a specific example for dynamically partitioned asset sensors attached to ops, so you may need to adapt this general approach to fit your requirements.
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