[GitHub] [superset] john-bodley commented on a change in pull request #15648: perf: Refactor Dashboard.datasets_trimmed_for_slices et al.

[GitBox <gi...@apache.org>]

john-bodley commented on a change in pull request #15648:
URL: https://github.com/apache/superset/pull/15648#discussion_r668382831



##########
File path: superset/models/dashboard.py
##########
@@ -246,12 +247,27 @@ def data(self) -> Dict[str, Any]:
         unless=lambda: not is_feature_enabled("DASHBOARD_CACHE"),
     )
     def datasets_trimmed_for_slices(self) -> List[Dict[str, Any]]:
-        datasource_slices = utils.indexed(self.slices, "datasource")
+
+        # Efficient manner of processing datasources associated with a dashboard. Rather
+        # than keying by the convenient `Slice.datasource` model (which results in a
+        # per slice database query), we lazily request datasource after deduping given
+        # that the same datasource could appear multiple times within a dashboard.
+        datasource_slices: Dict[
+            Tuple(Type["BaseDatasource"], int), Slice
+        ] = defaultdict(set)
+
+        for slc in self.slices:
+            datasource_slices[(slc.cls_model, slc.datasource_id)].add(slc)
+
         return [
             # Filter out unneeded fields from the datasource payload
             datasource.data_for_slices(slices)
-            for datasource, slices in datasource_slices.items()
-            if datasource
+            for (cls_model, datasource_id), slices in datasource_slices.items()
+            if (
+                datasource := db.session.query(cls_model)

Review comment:
       Loving the walrus. Sadly I later found out we needed to support Python 3.7.




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