How can I send an empty response while using BigQueryPandasIOManager? I want a table to be created only when a condition is satisfied.

When using the

BigQueryPandasIOManager

, if you want to conditionally create a table in BigQuery based on whether a certain condition is satisfied, you can control this behavior within your asset or op function. According to the documentation, to store data in BigQuery using the BigQuery I/O manager, you typically return a Pandas DataFrame from your asset, and Dagster will handle storing and loading your assets in BigQuery. However, if you want to prevent a table from being created when a DataFrame is empty or a condition is not met, you can implement a check within your asset or op function. If the condition is not satisfied, you can return an empty DataFrame or

None

. It's important to note that the documentation does not explicitly state the behavior of

BigQueryPandasIOManager

when an empty DataFrame or

None

is returned. Based on the issues reported by users, there have been discussions around handling empty DataFrames gracefully. For instance, one issue mentions that when an empty DataFrame is returned, the Snowflake Pandas IO manager errors because the internally called connector cannot create the table with no columns. This suggests that similar behavior might occur with

BigQueryPandasIOManager

, although it is not explicitly stated in the documentation. Here's a conceptual example based on the documentation's guidance on how you might implement such a condition within an asset:

python
from dagster import asset
import pandas as pd

@asset
def conditional_table(data: pd.DataFrame) -> pd.DataFrame:
    if my_condition_is_met(data):
        # Return the DataFrame to be stored in BigQuery
        return data
    else:
        # Return an empty DataFrame or None to avoid creating a table
        return pd.DataFrame()  # or return None

In this example,

my_condition_is_met

is a placeholder for whatever condition you want to check. If the condition is not met, the function returns an empty DataFrame or

None

, which should prevent the

BigQueryPandasIOManager

from creating a table. However, since the exact behavior with empty DataFrames or

None

is not detailed in the documentation, you may need to test this approach to ensure it works as expected in your specific use case. If you encounter issues or the behavior does not align with your expectations, you may need to consider alternative approaches or check for updates in the documentation or user discussions for any changes or recommended practices regarding this scenario. Skip creation of tables when dataframe r... button returning empty dataframes from assets/o... button Allow to CREATE OR REPLACE TABLE with du... button Dagster Docs button Thank you for your feedback!