partners/milvus: allow creating a vectorstore with sparse embeddings (l…

…angchain-ai#25284)

# Description
Milvus (and `pymilvus`) recently added the option to use [sparse
vectors](https://milvus.io/docs/sparse_vector.md#Sparse-Vector) with
appropriate search methods (e.g., `SPARSE_INVERTED_INDEX`) and
embeddings (e.g., `BM25`, `SPLADE`).

This PR allow creating a vector store using langchain's `Milvus` class,
setting the matching vector field type to `DataType.SPARSE_FLOAT_VECTOR`
and the default index type to `SPARSE_INVERTED_INDEX`.

It is only extending functionality, and backward compatible. 

## Note
I also interested in extending the Milvus class further to support multi
vector search (aka hybrid search). Will be happy to discuss that. See
[here](langchain-ai#19955),
[here](langchain-ai#20375), and
[here](langchain-ai#22886)
similar needs.

---------

Co-authored-by: Erick Friis <erick@langchain.dev>

libs/partners/milvus/langchain_milvus/vectorstores/milvus.py

@@ -1,14 +1,16 @@
 from __future__ import annotations
 
 import logging
-from typing import Any, Iterable, List, Optional, Tuple, Union
+from typing import Any, Dict, Iterable, List, Optional, Tuple, Union
 from uuid import uuid4
 
 import numpy as np
 from langchain_core.documents import Document
 from langchain_core.embeddings import Embeddings
 from langchain_core.vectorstores import VectorStore
 
+from langchain_milvus.utils.sparse import BaseSparseEmbedding
+
 logger = logging.getLogger(__name__)
 
 DEFAULT_MILVUS_CONNECTION = {
@@ -110,7 +112,7 @@ class Milvus(VectorStore):
             Name of the collection.
         collection_description: str
             Description of the collection.
-        embedding_function: Embeddings
+        embedding_function: Union[Embeddings, BaseSparseEmbedding]
             Embedding function to use.
 
     Key init args — client params:
@@ -219,7 +221,7 @@ class Milvus(VectorStore):
 
     def __init__(
         self,
-        embedding_function: Embeddings,
+        embedding_function: Union[Embeddings, BaseSparseEmbedding],  # type: ignore
         collection_name: str = "LangChainCollection",
         collection_description: str = "",
         collection_properties: Optional[dict[str, Any]] = None,
@@ -276,6 +278,11 @@ def __init__(
             },
             "GPU_IVF_FLAT": {"metric_type": "L2", "params": {"nprobe": 10}},
             "GPU_IVF_PQ": {"metric_type": "L2", "params": {"nprobe": 10}},
+            "SPARSE_INVERTED_INDEX": {
+                "metric_type": "IP",
+                "params": {"drop_ratio_build": 0.2},
+            },
+            "SPARSE_WAND": {"metric_type": "IP", "params": {"drop_ratio_build": 0.2}},
         }
 
         self.embedding_func = embedding_function
@@ -340,7 +347,7 @@ def __init__(
         )
 
     @property
-    def embeddings(self) -> Embeddings:
+    def embeddings(self) -> Union[Embeddings, BaseSparseEmbedding]:  # type: ignore
         return self.embedding_func
 
     def _create_connection_alias(self, connection_args: dict) -> str:
@@ -402,6 +409,10 @@ def _create_connection_alias(self, connection_args: dict) -> str:
             logger.error("Failed to create new connection using: %s", alias)
             raise e
 
+    @property
+    def _is_sparse_embedding(self) -> bool:
+        return isinstance(self.embedding_func, BaseSparseEmbedding)
+
     def _init(
         self,
         embeddings: Optional[list] = None,
@@ -539,9 +550,14 @@ def _create_collection(
                 )
             )
         # Create the vector field, supports binary or float vectors
-        fields.append(
-            FieldSchema(self._vector_field, infer_dtype_bydata(embeddings[0]), dim=dim)
-        )
+        if self._is_sparse_embedding:
+            fields.append(FieldSchema(self._vector_field, DataType.SPARSE_FLOAT_VECTOR))
+        else:
+            fields.append(
+                FieldSchema(
+                    self._vector_field, infer_dtype_bydata(embeddings[0]), dim=dim
+                )
+            )
 
         # Create the schema for the collection
         schema = CollectionSchema(
@@ -606,11 +622,18 @@ def _create_index(self) -> None:
             try:
                 # If no index params, use a default HNSW based one
                 if self.index_params is None:
-                    self.index_params = {
-                        "metric_type": "L2",
-                        "index_type": "HNSW",
-                        "params": {"M": 8, "efConstruction": 64},
-                    }
+                    if self._is_sparse_embedding:
+                        self.index_params = {
+                            "metric_type": "IP",
+                            "index_type": "SPARSE_INVERTED_INDEX",
+                            "params": {"drop_ratio_build": 0.2},
+                        }
+                    else:
+                        self.index_params = {
+                            "metric_type": "L2",
+                            "index_type": "HNSW",
+                            "params": {"M": 8, "efConstruction": 64},
+                        }
 
                 try:
                     self.col.create_index(
@@ -740,7 +763,7 @@ def add_texts(
                 )
 
         try:
-            embeddings = self.embedding_func.embed_documents(texts)
+            embeddings: list = self.embedding_func.embed_documents(texts)
         except NotImplementedError:
             embeddings = [self.embedding_func.embed_query(x) for x in texts]
 
@@ -815,7 +838,7 @@ def add_texts(
 
     def _collection_search(
         self,
-        embedding: List[float],
+        embedding: List[float] | Dict[int, float],
         k: int = 4,
         param: Optional[dict] = None,
         expr: Optional[str] = None,
@@ -829,7 +852,8 @@ def _collection_search(
         https://milvus.io/api-reference/pymilvus/v2.4.x/ORM/Collection/search.md
 
         Args:
-            embedding (List[float]): The embedding vector being searched.
+            embedding (List[float] | Dict[int, float]): The embedding vector being
+                searched.
             k (int, optional): The amount of results to return. Defaults to 4.
             param (dict): The search params for the specified index.
                 Defaults to None.
@@ -976,7 +1000,7 @@ def similarity_search_with_score(
 
     def similarity_search_with_score_by_vector(
         self,
-        embedding: List[float],
+        embedding: List[float] | Dict[int, float],
         k: int = 4,
         param: Optional[dict] = None,
         expr: Optional[str] = None,
@@ -990,7 +1014,8 @@ def similarity_search_with_score_by_vector(
         https://milvus.io/api-reference/pymilvus/v2.4.x/ORM/Collection/search.md
 
         Args:
-            embedding (List[float]): The embedding vector being searched.
+            embedding (List[float] | Dict[int, float]): The embedding vector being
+                searched.
             k (int, optional): The amount of results to return. Defaults to 4.
             param (dict): The search params for the specified index.
                 Defaults to None.
@@ -1068,7 +1093,7 @@ def max_marginal_relevance_search(
 
     def max_marginal_relevance_search_by_vector(
         self,
-        embedding: list[float],
+        embedding: list[float] | dict[int, float],
         k: int = 4,
         fetch_k: int = 20,
         lambda_mult: float = 0.5,
@@ -1080,7 +1105,8 @@ def max_marginal_relevance_search_by_vector(
         """Perform a search and return results that are reordered by MMR.
 
         Args:
-            embedding (str): The embedding vector being searched.
+            embedding (list[float] | dict[int, float]): The embedding vector being
+                searched.
             k (int, optional): How many results to give. Defaults to 4.
             fetch_k (int, optional): Total results to select k from.
                 Defaults to 20.
@@ -1171,7 +1197,7 @@ def delete(  # type: ignore[no-untyped-def]
     def from_texts(
         cls,
         texts: List[str],
-        embedding: Embeddings,
+        embedding: Union[Embeddings, BaseSparseEmbedding],  # type: ignore
         metadatas: Optional[List[dict]] = None,
         collection_name: str = "LangChainCollection",
         connection_args: dict[str, Any] = DEFAULT_MILVUS_CONNECTION,
@@ -1187,7 +1213,7 @@ def from_texts(
 
         Args:
             texts (List[str]): Text data.
-            embedding (Embeddings): Embedding function.
+            embedding (Union[Embeddings, BaseSparseEmbedding]): Embedding function.
             metadatas (Optional[List[dict]]): Metadata for each text if it exists.
                 Defaults to None.
             collection_name (str, optional): Collection name to use. Defaults to

libs/partners/milvus/langchain_milvus/vectorstores/zilliz.py

@@ -1,10 +1,11 @@
 from __future__ import annotations
 
 import logging
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, List, Optional, Union
 
 from langchain_core.embeddings import Embeddings
 
+from langchain_milvus.utils.sparse import BaseSparseEmbedding
 from langchain_milvus.vectorstores.milvus import Milvus
 
 logger = logging.getLogger(__name__)
@@ -141,7 +142,7 @@ def _create_index(self) -> None:
     def from_texts(
         cls,
         texts: List[str],
-        embedding: Embeddings,
+        embedding: Union[Embeddings, BaseSparseEmbedding],
         metadatas: Optional[List[dict]] = None,
         collection_name: str = "LangChainCollection",
         connection_args: Optional[Dict[str, Any]] = None,

libs/partners/milvus/tests/integration_tests/vectorstores/test_milvus.py

@@ -5,6 +5,7 @@
 import pytest
 from langchain_core.documents import Document
 
+from langchain_milvus.utils.sparse import BM25SparseEmbedding
 from langchain_milvus.vectorstores import Milvus
 from tests.integration_tests.utils import (
     FakeEmbeddings,
@@ -304,6 +305,31 @@ def test_milvus_enable_dynamic_field_with_partition_key() -> None:
     }
 
 
+def test_milvus_sparse_embeddings() -> None:
+    texts = [
+        "In 'The Clockwork Kingdom' by Augusta Wynter, a brilliant inventor discovers "
+        "a hidden world of clockwork machines and ancient magic, where a rebellion is "
+        "brewing against the tyrannical ruler of the land.",
+        "In 'The Phantom Pilgrim' by Rowan Welles, a charismatic smuggler is hired by "
+        "a mysterious organization to transport a valuable artifact across a war-torn "
+        "continent, but soon finds themselves pursued by assassins and rival factions.",
+        "In 'The Dreamwalker's Journey' by Lyra Snow, a young dreamwalker discovers "
+        "she has the ability to enter people's dreams, but soon finds herself trapped "
+        "in a surreal world of nightmares and illusions, where the boundaries between "
+        "reality and fantasy blur.",
+    ]
+    sparse_embedding_func = BM25SparseEmbedding(corpus=texts)
+    docsearch = Milvus.from_texts(
+        embedding=sparse_embedding_func,
+        texts=texts,
+        connection_args={"uri": "./milvus_demo.db"},
+        drop_old=True,
+    )
+
+    output = docsearch.similarity_search("Pilgrim", k=1)
+    assert "Pilgrim" in output[0].page_content
+
+
 def test_milvus_array_field() -> None:
     """Manually specify metadata schema, including an array_field.
     For more information about array data type and filtering, please refer to
@@ -365,4 +391,6 @@ def test_milvus_array_field() -> None:
 #     test_milvus_enable_dynamic_field()
 #     test_milvus_disable_dynamic_field()
 #     test_milvus_metadata_field()
+#     test_milvus_enable_dynamic_field_with_partition_key()
+#     test_milvus_sparse_embeddings()
 #     test_milvus_array_field()