Fix pandas_to_eland append to an aliased index

CHANGELOG.rst

@@ -2,6 +2,11 @@
 Changelog
 =========
 
+Unreleased
+----------
+
+* Fix ``pandas_to_eland`` failing to append to an aliased index (`#829 <https://github.com/elastic/eland/pull/829>`_)
+
 9.2.0 (2025-10-30)
 ------------------
 

eland/etl.py

@@ -179,14 +179,18 @@ def pandas_to_eland(
             es_client.indices.create(index=es_dest_index, mappings=mapping["mappings"])
 
         elif es_if_exists == "append" and es_verify_mapping_compatibility:
-            dest_mapping = es_client.indices.get_mapping(index=es_dest_index)[
-                es_dest_index
-            ]
-            verify_mapping_compatibility(
-                ed_mapping=mapping,
-                es_mapping=dest_mapping,
-                es_type_overrides=es_type_overrides,
-            )
+            # get_mapping keys its response by concrete index name, which differs
+            # from es_dest_index when it is an alias. Verify against every index
+            # the name resolves to rather than assuming the response is keyed by
+            # es_dest_index (which raised KeyError for an alias, see #747).
+            for dest_mapping in es_client.indices.get_mapping(
+                index=es_dest_index
+            ).values():
+                verify_mapping_compatibility(
+                    ed_mapping=mapping,
+                    es_mapping=dest_mapping,
+                    es_type_overrides=es_type_overrides,
+                )
     else:
         es_client.indices.create(index=es_dest_index, mappings=mapping["mappings"])
 

tests/etl/test_pandas_to_eland.py

@@ -138,6 +138,34 @@ def test_es_if_exists_append(self):
         pd_df3 = pd_df._append(pd_df2)
         assert_pandas_eland_frame_equal(pd_df3, df2)
 
+    def test_es_if_exists_append_to_alias(self):
+        # Regression for #747: appending through an alias used to fail with
+        # KeyError, because get_mapping keys its response by the concrete index
+        # name rather than by the alias passed as es_dest_index.
+        pandas_to_eland(
+            pd_df,
+            es_client=ES_TEST_CLIENT,
+            es_dest_index="test-index",
+            es_refresh=True,
+        )
+        ES_TEST_CLIENT.indices.put_alias(index="test-index", name="test-alias")
+
+        try:
+            df = pandas_to_eland(
+                pd_df,
+                es_client=ES_TEST_CLIENT,
+                es_dest_index="test-alias",
+                es_if_exists="append",
+                es_refresh=True,
+            )
+
+            # Both writes landed in the aliased index.
+            assert df.shape == (6, 4)
+        finally:
+            ES_TEST_CLIENT.indices.delete_alias(
+                index="test-index", name="test-alias", ignore=404
+            )
+
     def test_es_if_exists_append_mapping_mismatch_schema_enforcement(self):
         df1 = pandas_to_eland(
             pd_df,