[GitHub] [airflow] ashb commented on a diff in pull request #24101: Add a new 'item' field to TaskMap

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

ashb commented on code in PR #24101:
URL: https://github.com/apache/airflow/pull/24101#discussion_r891174401


##########
airflow/models/taskinstance.py:
##########
@@ -2272,19 +2271,20 @@ def _record_task_map_for_downstreams(self, task: "Operator", value: Any, *, sess
         # currently possible for a downstream to depend on one individual mapped
         # task instance, only a task as a whole. This will change in AIP-42
         # Phase 2, and we'll need to further analyze the mapped task case.
-        if next(task.iter_mapped_dependants(), None) is None:
-            return
-        if value is None:
-            raise XComForMappingNotPushed()
         if task.is_mapped:
+            # But we still need to check the mapped task did push something for
+            # its downstream tasks...
+            if next(task.iter_mapped_dependants(), None) is not None and value is None:
+                raise XComForMappingNotPushed()
+            return
+
+        it1, it2 = itertools.tee(task.iter_mapped_dependants())
+        if next(it1, None) is None:  # No children need to expand, don't bother recording.
             return
-        if not isinstance(value, collections.abc.Collection) or isinstance(value, (bytes, str)):
-            raise UnmappableXComTypePushed(value)
-        task_map = TaskMap.from_task_instance_xcom(self, value)
-        max_map_length = conf.getint("core", "max_map_length", fallback=1024)
-        if task_map.length > max_map_length:
-            raise UnmappableXComLengthPushed(value, max_map_length)
-        session.merge(task_map)
+        session.merge(TaskMap.from_task_instance_xcom(self, value, item=""))
+        if isinstance(value, dict) and any(node.should_unpack_mapped_kwargs() for node in it2):
+            for task_map in TaskMap.from_unpacking_task_instance_xcom(self, value):
+                session.merge(task_map)

Review Comment:
   Why do we create both `item=""` and item set to something here?



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