core[minor]: add **kwargs to index and aindex functions for custom vector_field support (#26998)

Added `**kwargs` parameters to the `index` and `aindex` functions in
`libs/core/langchain_core/indexing/api.py`. This allows users to pass
additional arguments to the `add_documents` and `aadd_documents`
methods, enabling the specification of a custom `vector_field`. For
example, users can now use `vector_field="embedding"` when indexing
documents in `OpenSearchVectorStore`

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

libs/core/tests/unit_tests/indexing/test_indexing.py

@@ -7,6 +7,7 @@ from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
 import pytest_asyncio
+from pytest_mock import MockerFixture
 
 from langchain_core.document_loaders.base import BaseLoader
 from langchain_core.documents import Document
@@ -1728,3 +1729,180 @@ async def test_incremental_aindexing_with_batch_size_with_optimization(
         for uid in vector_store.store
     }
     assert doc_texts == {"updated 1", "2", "3", "updated 4"}
+
+
+def test_index_with_upsert_kwargs(
+    record_manager: InMemoryRecordManager, upserting_vector_store: InMemoryVectorStore
+) -> None:
+    """Test indexing with upsert_kwargs parameter."""
+    mock_add_documents = MagicMock()
+
+    with patch.object(upserting_vector_store, "add_documents", mock_add_documents):
+        docs = [
+            Document(
+                page_content="Test document 1",
+                metadata={"source": "1"},
+            ),
+            Document(
+                page_content="Test document 2",
+                metadata={"source": "2"},
+            ),
+        ]
+
+        upsert_kwargs = {"vector_field": "embedding"}
+
+        index(docs, record_manager, upserting_vector_store, upsert_kwargs=upsert_kwargs)
+
+        # Assert that add_documents was called with the correct arguments
+        mock_add_documents.assert_called_once()
+        call_args = mock_add_documents.call_args
+        assert call_args is not None
+        args, kwargs = call_args
+
+        # Check that the documents are correct (ignoring ids)
+        assert len(args[0]) == 2
+        assert all(isinstance(doc, Document) for doc in args[0])
+        assert [doc.page_content for doc in args[0]] == [
+            "Test document 1",
+            "Test document 2",
+        ]
+        assert [doc.metadata for doc in args[0]] == [{"source": "1"}, {"source": "2"}]
+
+        # Check that ids are present
+        assert "ids" in kwargs
+        assert isinstance(kwargs["ids"], list)
+        assert len(kwargs["ids"]) == 2
+
+        # Check other arguments
+        assert kwargs["batch_size"] == 100
+        assert kwargs["vector_field"] == "embedding"
+
+
+def test_index_with_upsert_kwargs_for_document_indexer(
+    record_manager: InMemoryRecordManager,
+    mocker: MockerFixture,
+) -> None:
+    """Test that kwargs are passed to the upsert method of the document indexer."""
+
+    document_index = InMemoryDocumentIndex()
+    upsert_spy = mocker.spy(document_index.__class__, "upsert")
+    docs = [
+        Document(
+            page_content="This is a test document.",
+            metadata={"source": "1"},
+        ),
+        Document(
+            page_content="This is another document.",
+            metadata={"source": "2"},
+        ),
+    ]
+
+    upsert_kwargs = {"vector_field": "embedding"}
+
+    assert index(
+        docs,
+        record_manager,
+        document_index,
+        cleanup="full",
+        upsert_kwargs=upsert_kwargs,
+    ) == {
+        "num_added": 2,
+        "num_deleted": 0,
+        "num_skipped": 0,
+        "num_updated": 0,
+    }
+
+    assert upsert_spy.call_count == 1
+    # assert call kwargs were passed as kwargs
+    assert upsert_spy.call_args.kwargs == upsert_kwargs
+
+
+async def test_aindex_with_upsert_kwargs_for_document_indexer(
+    arecord_manager: InMemoryRecordManager,
+    mocker: MockerFixture,
+) -> None:
+    """Test that kwargs are passed to the upsert method of the document indexer."""
+
+    document_index = InMemoryDocumentIndex()
+    upsert_spy = mocker.spy(document_index.__class__, "aupsert")
+    docs = [
+        Document(
+            page_content="This is a test document.",
+            metadata={"source": "1"},
+        ),
+        Document(
+            page_content="This is another document.",
+            metadata={"source": "2"},
+        ),
+    ]
+
+    upsert_kwargs = {"vector_field": "embedding"}
+
+    assert await aindex(
+        docs,
+        arecord_manager,
+        document_index,
+        cleanup="full",
+        upsert_kwargs=upsert_kwargs,
+    ) == {
+        "num_added": 2,
+        "num_deleted": 0,
+        "num_skipped": 0,
+        "num_updated": 0,
+    }
+
+    assert upsert_spy.call_count == 1
+    # assert call kwargs were passed as kwargs
+    assert upsert_spy.call_args.kwargs == upsert_kwargs
+
+
+async def test_aindex_with_upsert_kwargs(
+    arecord_manager: InMemoryRecordManager, upserting_vector_store: InMemoryVectorStore
+) -> None:
+    """Test async indexing with upsert_kwargs parameter."""
+    mock_aadd_documents = AsyncMock()
+
+    with patch.object(upserting_vector_store, "aadd_documents", mock_aadd_documents):
+        docs = [
+            Document(
+                page_content="Async test document 1",
+                metadata={"source": "1"},
+            ),
+            Document(
+                page_content="Async test document 2",
+                metadata={"source": "2"},
+            ),
+        ]
+
+        upsert_kwargs = {"vector_field": "embedding"}
+
+        await aindex(
+            docs,
+            arecord_manager,
+            upserting_vector_store,
+            upsert_kwargs=upsert_kwargs,
+        )
+
+        # Assert that aadd_documents was called with the correct arguments
+        mock_aadd_documents.assert_called_once()
+        call_args = mock_aadd_documents.call_args
+        assert call_args is not None
+        args, kwargs = call_args
+
+        # Check that the documents are correct (ignoring ids)
+        assert len(args[0]) == 2
+        assert all(isinstance(doc, Document) for doc in args[0])
+        assert [doc.page_content for doc in args[0]] == [
+            "Async test document 1",
+            "Async test document 2",
+        ]
+        assert [doc.metadata for doc in args[0]] == [{"source": "1"}, {"source": "2"}]
+
+        # Check that ids are present
+        assert "ids" in kwargs
+        assert isinstance(kwargs["ids"], list)
+        assert len(kwargs["ids"]) == 2
+
+        # Check other arguments
+        assert kwargs["batch_size"] == 100
+        assert kwargs["vector_field"] == "embedding"