Revert "core[patch]: improve index/aindex api when batch_size<n_docs (l…

…angchain-ai#25754)"

This reverts commit 2538963.

libs/core/langchain_core/indexing/api.py

@@ -408,18 +408,16 @@ def index(
 
             # mypy isn't good enough to determine that source ids cannot be None
             # here due to a check that's happening above, so we check again.
-            if any(source_id is None for source_id in source_ids):
-                msg = "Source ids cannot be if cleanup=='incremental'."
-                raise AssertionError(msg)
+            for source_id in source_ids:
+                if source_id is None:
+                    raise AssertionError("Source ids cannot be None here.")
 
-            indexed_source_ids = cast(
-                Sequence[str], [source_id_assigner(doc) for doc in docs_to_index]
-            )
+            _source_ids = cast(Sequence[str], source_ids)
 
             uids_to_delete = record_manager.list_keys(
-                group_ids=indexed_source_ids, before=index_start_dt
+                group_ids=_source_ids, before=index_start_dt
             )
-            if indexed_source_ids and uids_to_delete:
+            if uids_to_delete:
                 # Then delete from vector store.
                 destination.delete(uids_to_delete)
                 # First delete from record store.
@@ -669,18 +667,16 @@ async def aindex(
 
             # mypy isn't good enough to determine that source ids cannot be None
             # here due to a check that's happening above, so we check again.
-            if any(source_id is None for source_id in source_ids):
-                msg = "Source ids cannot be if cleanup=='incremental'."
-                raise AssertionError(msg)
+            for source_id in source_ids:
+                if source_id is None:
+                    raise AssertionError("Source ids cannot be None here.")
 
-            indexed_source_ids = cast(
-                Sequence[str], [source_id_assigner(doc) for doc in docs_to_index]
-            )
+            _source_ids = cast(Sequence[str], source_ids)
 
             uids_to_delete = await record_manager.alist_keys(
-                group_ids=indexed_source_ids, before=index_start_dt
+                group_ids=_source_ids, before=index_start_dt
             )
-            if indexed_source_ids and uids_to_delete:
+            if uids_to_delete:
                 # Then delete from vector store.
                 await destination.adelete(uids_to_delete)
                 # First delete from record store.