@Scout how do I map a multi-dimensional partitioned asset to a single dimension partitioned asset, where second asset's partition is uses only the primary partition of the first asset?

To map a multi-dimensional partitioned asset to a single-dimension partitioned asset, where the second asset uses only the primary partition of the first asset, you can use the

MultiToSingleDimensionPartitionMapping

provided by Dagster. This partition mapping assumes that any multi-partition key with the specified dimension in the selected dimension is a dependency for the single-dimension partitioned asset. Here's an example from the documentation that illustrates how you might define such a relationship:

python from dagster import (     DynamicPartitionsDefinition,     WeeklyPartitionsDefinition,     asset,     MultiPartitionsDefinition, )  projects_partitions_def = DynamicPartitionsDefinition(name="project") # a, b, c  @asset(     partitions_def=MultiPartitionsDefinition(         partitions_defs={             "week": WeeklyPartitionsDefinition("2023-01-01"),             "project": projects_partitions_def,         }     ) ) def upstream():     ...  @asset(partitions_def=projects_partitions_def) def downstream(context, upstream):     ...

In this example, when you execute the

downstream

asset with a specific partition (e.g., partition "a"), it will load every partition of the

upstream

asset that has "a" as its project dimension:

a|2023-01-01

,

a|2023-01-08

, etc. This is because the

projects_partitions_def

is used as the partitions definition for both the multi-partitioned

upstream

asset and the single-dimension

downstream

asset. Dagster automatically uses the

MultiToSingleDimensionPartitionMapping

to map the dependencies correctly. If you need to customize the partition mapping further, you can define your own partition mapping class by subclassing

PartitionMapping

and implementing the necessary methods to specify the exact mapping logic you require. However, the example above should suffice for the case where you want to map the primary dimension of a multi-dimensional partitioned asset to a single-dimension partitioned asset.