https://dagster.io/ logo
#ask-ai
Title
# ask-ai
m

Marcel Steinbach

02/21/2024, 9:05 AM
@Scout I have partitioned assets A and B, where B depends on A with the same partition. I need to make sure that if I backfill B, that partition A is materialized.
s

Scout

02/21/2024, 9:05 AM
When you backfill a partitioned asset in Dagster, the system respects the dependencies between assets. If asset B depends on asset A with the same partition, and you initiate a backfill for asset B, Dagster will ensure that the corresponding partition of asset A is materialized first before materializing asset B. The documentation mentions that orchestrators, which are responsible for tracking dependencies in data pipelines, can be helpful for managing these kinds of backfills. They can kick off work to backfill the downstream table (asset B in your case) after the backfill of the upstream table (asset A) is complete. Additionally, the documentation states that when you define a graph of partitioned assets, you can kick off runs that materialize the same partition across a set of assets. This means that if you have a dependency from asset B to asset A, and you launch a backfill for asset B, Dagster will recognize that asset A needs to be materialized first for the corresponding partition. It's important to note that the behavior of respecting partition dependencies during backfills is something that Dagster handles as part of its orchestration capabilities. If you encounter any issues where dependencies are not being respected as expected during a backfill, it would be advisable to check the configuration of your assets and their dependencies to ensure they are defined correctly. If the problem persists, you might want to consult the Dagster community or support channels for further assistance.
m

Marcel Steinbach

02/21/2024, 9:12 AM
@Scout how do I need to define the dependency so this works? this doesn't work
Copy code
@asset(
        deps=[A],
    )
s

Scout

02/21/2024, 9:12 AM
To define dependencies between partitioned assets in Dagster, you should ensure that the dependencies are set up correctly using the
@asset
decorator. The
deps
parameter should be used to specify the dependencies of an asset. However, if you're encountering issues with the simple
deps=[A]
declaration, it might be due to how the assets are being recognized by Dagster. Here's a basic example of how to define dependencies between assets:
Copy code
python from dagster import asset  @asset def A():     # logic for asset A     pass  @asset(deps=[A]) def B(A_result):     # logic for asset B that depends on A     pass
In this example,
B
depends on
A
, and the dependency is declared in the
@asset
decorator of
B
using
deps=[A]
. Additionally, the function
B
takes an argument
A_result
, which corresponds to the output of asset
A
. This is how Dagster knows to pass the output of
A
to
B
. If you're working with partitioned assets, you need to ensure that the partitions are correctly defined and that the dependencies respect those partitions. Here's an example of how you might define partitioned assets with dependencies:
Copy code
python from dagster import asset, DailyPartitionsDefinition  partitions_def = DailyPartitionsDefinition(start_date="2021-01-01")  @asset(partitions_def=partitions_def) def A():     # logic for asset A     pass  @asset(partitions_def=partitions_def, deps=[A]) def B(A_result):     # logic for asset B that depends on A     pass
In this case, both
A
and
B
are defined with the same
DailyPartitionsDefinition
, which means they will have corresponding partitions for each day starting from "2021-01-01". If you're still encountering issues, make sure that: 1. The partition definitions for both assets are compatible and aligned. 2. The assets are correctly registered in your repository. 3. You're using the correct version of Dagster that supports the features you're using. If the problem persists, you may want to check the Dagster documentation for the most up-to-date information on defining dependencies between partitioned assets or seek help from the Dagster community.