Support asset backfills in UI that target only unpartitioned assets (#…

…18352)

Fixes #15173

Previously, a graphQL error would be raised when attempting to display a
backfill that targets only unpartitioned assets. This is because we
assumed in a resolver that at least 1 partition would be targeted.

This PR fixes the issue:

<img width="1450" alt="image"
src="https://github.com/dagster-io/dagster/assets/29110579/3916e1ed-5660-462b-a730-e352461e68b6">

I also went through the UI and confirmed that all other pages were
displaying correctly, so looks like this is the only spot where we
assume partitioned asset(s) are targeted by the backfill.

js_modules/dagster-ui/packages/ui-core/src/instance/backfill/TargetPartitionsDisplay.tsx

@@ -13,7 +13,7 @@ export const TargetPartitionsDisplay = ({
   targetPartitions,
 }: {
   targetPartitionCount?: number;
-  targetPartitions?: Pick<AssetBackfillTargetPartitions, 'partitionKeys' | 'ranges'>;
+  targetPartitions?: Pick<AssetBackfillTargetPartitions, 'partitionKeys' | 'ranges'> | null;
 }) => {
   const [isDialogOpen, setIsDialogOpen] = React.useState(false);
 
@@ -95,6 +95,12 @@ export const TargetPartitionsDisplay = ({
   }
 
   return (
-    <div>{targetPartitionCount === 1 ? '1 partition' : `${targetPartitionCount} partitions`}</div>
+    <div>
+      {targetPartitionCount === 0
+        ? '-'
+        : targetPartitionCount === 1
+        ? '1 partition'
+        : `${targetPartitionCount} partitions`}
+    </div>
   );
 };

python_modules/dagster-graphql/dagster_graphql/schema/backfill.py

@@ -171,7 +171,7 @@ class Meta:
     assetBackfillStatuses = non_null_list(
         "dagster_graphql.schema.partition_sets.GrapheneAssetBackfillStatus"
     )
-    rootTargetedPartitions = graphene.NonNull(
+    rootTargetedPartitions = graphene.Field(
         "dagster_graphql.schema.backfill.GrapheneAssetBackfillTargetPartitions",
     )
 

python_modules/dagster-graphql/dagster_graphql_tests/graphql/test_asset_backfill.py

@@ -762,6 +762,49 @@ def test_launch_asset_backfill_with_upstream_anchor_asset_and_non_partitioned_as
             assert targeted_ranges[0]["end"] == "2020-01-03-00:00"
 
 
+def test_asset_backfill_status_only_unpartitioned_assets():
+    repo = get_daily_hourly_non_partitioned_repo()
+
+    with instance_for_test() as instance:
+        with define_out_of_process_context(
+            __file__, "get_daily_hourly_non_partitioned_repo", instance
+        ) as context:
+            # launchPartitionBackfill
+            launch_backfill_result = execute_dagster_graphql(
+                context,
+                LAUNCH_PARTITION_BACKFILL_MUTATION,
+                variables={
+                    "backfillParams": {
+                        "allPartitions": True,
+                        "assetSelection": [AssetKey("non_partitioned").to_graphql_input()],
+                    }
+                },
+            )
+            backfill_id, asset_backfill_data = _get_backfill_data(
+                launch_backfill_result, instance, repo
+            )
+            target_subset = asset_backfill_data.target_subset
+
+            assert target_subset == AssetGraphSubset(
+                non_partitioned_asset_keys={AssetKey("non_partitioned")},
+            )
+
+            asset_backfill_data_result = execute_dagster_graphql(
+                context, ASSET_BACKFILL_DATA_QUERY, variables={"backfillId": backfill_id}
+            )
+            assert asset_backfill_data_result.data
+            assert (
+                asset_backfill_data_result.data["partitionBackfillOrError"]["isAssetBackfill"]
+                is True
+            )
+            assert (
+                asset_backfill_data_result.data["partitionBackfillOrError"]["assetBackfillData"][
+                    "rootTargetedPartitions"
+                ]
+                is None
+            )
+
+
 def test_asset_backfill_preview_time_partitioned():
     repo = get_daily_hourly_non_partitioned_repo()
     all_asset_keys = repo.asset_graph.materializable_asset_keys

python_modules/dagster/dagster/_core/execution/asset_backfill.py

@@ -267,7 +267,9 @@ def get_target_partitions_subset(self, asset_key: AssetKey) -> PartitionsSubset:
         # Return the targeted partitions for the root partitioned asset keys
         return self.target_subset.get_partitions_subset(asset_key)
 
-    def get_target_root_partitions_subset(self, asset_graph: AssetGraph) -> PartitionsSubset:
+    def get_target_root_partitions_subset(
+        self, asset_graph: AssetGraph
+    ) -> Optional[PartitionsSubset]:
         """Returns the most upstream partitions subset that was targeted by the backfill."""
         partitioned_asset_keys = {
             asset_key
@@ -280,7 +282,10 @@ def get_target_root_partitions_subset(self, asset_graph: AssetGraph) -> Partitio
         )
 
         # Return the targeted partitions for the root partitioned asset keys
-        return self.target_subset.get_partitions_subset(next(iter(root_partitioned_asset_keys)))
+        if root_partitioned_asset_keys:
+            return self.target_subset.get_partitions_subset(next(iter(root_partitioned_asset_keys)))
+
+        return None
 
     def get_num_partitions(self) -> Optional[int]:
         """Only valid when the same number of partitions are targeted in every asset.