I wish to setup my asset (Asset B) to depend on an earlier partition of an upstream asset (Asset A), in order to comply with the error:

"Assets can only depend on themselves if they are:
(a) time-partitioned and each partition depends on earlier partitions"

How can I do that? Show me an example.

To set up your asset (Asset B) to depend on an earlier partition of an upstream asset (Asset A), you can use a

TimeWindowPartitionMapping

to specify that each partition of Asset B should depend on the prior partition of Asset A. Here's an example from the documentation that demonstrates how to do this:

python from dagster import (     AssetDep,     DailyPartitionsDefinition,     TimeWindowPartitionMapping,     asset, )  partitions_def = DailyPartitionsDefinition(start_date="2023-01-21")  @asset(partitions_def=partitions_def) def asset_a():     ...  @asset(     partitions_def=partitions_def,     deps=[         AssetDep(             asset_a,             partition_mapping=TimeWindowPartitionMapping(                 start_offset=-1, end_offset=-1             ),         )     ], ) def asset_b():     ...

In this example,

asset_a

is defined with a daily partition starting from a specific date.

asset_b

is defined to depend on

asset_a

, and the

TimeWindowPartitionMapping

is used to specify that each partition of

asset_b

should depend on the prior day's partition of

asset_a

. The

start_offset

and

end_offset

are both set to

-1

, indicating that

asset_b

depends on the partition of

asset_a

from one day earlier.

@Scout I tried implementing the above. asset_a materialized without issue but I'm getting an error when materializing asset_b:

dagster._check.CheckError: Failure condition: downstream_partitions_subset must be a BaseTimeWindowPartitionsSubset

What is the issue?

The error message you're encountering,

Failure condition: downstream_partitions_subset must be a BaseTimeWindowPartitionsSubset

, suggests that there is a mismatch between the expected partition subset type and the one being provided during the materialization process of

asset_b

. This error could occur if the partition mapping is not set up correctly or if there is an issue with how the partitions are defined for

asset_b

. The

TimeWindowPartitionMapping

expects that the partitions of both the upstream and downstream assets are defined in a way that is compatible with time window partitioning. To resolve this issue, ensure the following: 1. Both

asset_a

and

asset_b

have compatible partition definitions. If they are using

DailyPartitionsDefinition

, they should both be configured with the same start date and frequency. 2. The

TimeWindowPartitionMapping

is correctly configured with the appropriate offsets to map the partitions from

asset_a

to

asset_b

. 3. When materializing

asset_b

, you are providing a valid partition key that exists within the defined partitions. If you've verified these points and the issue persists, it could be helpful to review the full stack trace of the error and check the partition definitions and materialization logic for any discrepancies. If the problem is not immediately apparent, you may need to provide more context or seek further assistance from the Dagster community or support channels, as the error might be specific to your implementation details or environment.