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# ask-ai
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Peter Mburu

03/05/2024, 8:05 AM
@Scout How to get asset metadata from materialize
s

Scout

03/05/2024, 8:05 AM
To get asset metadata from a materialization in Dagster, you can use the
AssetMaterialization
event to attach metadata to an asset when it is materialized. This metadata can then be accessed in various ways, depending on where you need to use it. Here's an example of how you might emit an
AssetMaterialization
event with metadata when materializing an asset:
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python from dagster import AssetMaterialization, MetadataValue, op, OpExecutionContext  @op def my_metadata_materialization_op(context: OpExecutionContext):     df = read_df()     remote_storage_path = persist_to_storage(df)     context.log_event(         AssetMaterialization(             asset_key="my_dataset",             description="Persisted result to storage",             metadata={                 "text_metadata": "Text-based metadata for this event",                 "path": MetadataValue.path(remote_storage_path),                 "dashboard_url": MetadataValue.url(                     "<http://mycoolsite.com/url_for_my_data>"                 ),                 "size (bytes)": calculate_bytes(df),             },         )     )     return remote_storage_path
In this example, the
my_metadata_materialization_op
op reads some data, persists it to storage, and then logs an
AssetMaterialization
event with metadata about the storage path, a URL to a dashboard, and the size of the data in bytes. To access this metadata later, you can use the Dagster instance to query the event log for materialization events. Here's an example of how you might do this within another asset:
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python from dagster import asset, AssetKey, DagsterInstance  @asset def downstream_asset():     instance = DagsterInstance.get()     materialization = instance.get_latest_materialization_event(AssetKey(["my_dataset"])).asset_materialization     metadata = materialization.metadata     # Now you can use the metadata as needed
In this example,
downstream_asset
uses the
DagsterInstance.get()
method to get the current Dagster instance and then queries for the latest materialization event for the asset with the key
my_dataset
. It then accesses the metadata from this materialization event. Please note that the exact method to access the metadata may vary depending on the context in which you're working (e.g., within an asset, op, or sensor) and whether the asset is partitioned or not. The provided examples are based on the documentation and should be adapted to fit the specific requirements of your Dagster project.
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