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# ask-ai
p

Paul Herzog

02/26/2024, 6:46 PM
@Scout in Asset Catalog there is a field "Column" -> "Dagster can render an assets column schema once it has been materialized. Metadata" how can i provide schema?
s

Scout

02/26/2024, 6:46 PM
To provide a schema for an asset in Dagster, you can use the
MetadataValue
class to attach schema information to the asset's materialization metadata. This metadata, including the column names and data types, can be rendered in the Dagster UI once the asset has been materialized. Here's an example from the documentation on how to add table schema metadata to an asset:
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python from dagster import asset, MetadataValue, AssetMaterialization import pandas as pd from dagster_pandas import create_dagster_pandas_dataframe_type  @asset def my_asset():     data = pd.DataFrame({         "column1": [1, 2, 3],         "column2": ["a", "b", "c"]     })          yield AssetMaterialization(         description="my_asset materialization",         metadata={             "table_schema": create_dagster_pandas_dataframe_type(data)         }     )          yield Output(data)
In this example,
create_dagster_pandas_dataframe_type
is a utility function from the
dagster_pandas
library that generates a
TableSchemaMetadataValue
based on the provided DataFrame. This metadata value includes the column names and data types, which Dagster can then render in the asset catalog. Please note that the exact function or method to create the schema metadata may vary depending on the version of Dagster and the libraries you are using. Always refer to the latest documentation for the most up-to-date information and examples.
p

Paul Herzog

02/27/2024, 12:30 PM
This didnt work. is there a different way? @Scout
s

Scout

02/27/2024, 12:30 PM
I apologize for the confusion earlier. If the method I provided did not work, it's possible that the approach to attaching schema metadata to an asset has changed or that additional context is needed for your specific use case. In Dagster, you can attach metadata to assets using the
@asset
decorator and by yielding
AssetMaterialization
objects with metadata. However, the specific way to attach a schema to an asset's columns is not detailed in the documentation I have access to. Here's a more general example of how you might attach metadata to an asset:
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python from dagster import asset, MetadataEntry, Output  @asset def my_asset():     # Your asset computation logic here     result = compute_something()          # Define metadata entries for your asset     metadata_entries = [         MetadataEntry("key", value="value", description="Description of the metadata entry"),         # Add more metadata entries as needed     ]          # Yield an AssetMaterialization with the metadata entries     yield AssetMaterialization(description="Description of my asset", metadata_entries=metadata_entries)          # Yield the result of the asset computation     yield Output(result)
In this example,
MetadataEntry
is used to define individual pieces of metadata. You would replace
"key"
,
"value"
, and
"Description of the metadata entry"
with the appropriate schema information for your asset. If you are looking to provide a detailed schema, such as column types and other properties, and the above method does not meet your needs, I recommend checking the following: 1. Dagster Version: Ensure you are using a version of Dagster that supports the features you are trying to use. The Dagster API can evolve, and newer versions may have different ways of handling metadata. 2. Documentation: Review the latest [Dagster documentation](https://docs.dagster.io/) for assets and metadata. There may be updated guidance on how to attach schema metadata to assets. 3. Community and Support: If the documentation does not provide a clear answer, consider reaching out to the Dagster community through [GitHub Discussions](https://github.com/dagster-io/dagster/discussions) or the [Dagster Slack](https://dagster.io/slack) for more specific guidance. 4. Custom Metadata Entries: If Dagster does not provide a built-in way to represent a column schema, you may need to create custom metadata entries that represent your schema and attach them to your asset materializations. If you continue to encounter difficulties, please provide more details about what you are trying to achieve, including any error messages or unexpected behavior, so that I can offer more targeted assistance.
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