Chroma persistence (#1028)

This PR adds persistence to the Chroma vector store.

Users can supply a `persist_directory` with any of the `Chroma` creation
methods. If supplied, the store will be automatically persisted at that
directory.

If a user creates a new `Chroma` instance with the same persistence
directory, it will get loaded up automatically. If they use `from_texts`
or `from_documents` in this way, the documents will be loaded into the
existing store.

There is the chance of some funky behavior if the user passes a
different embedding function from the one used to create the collection
- we will make this easier in future updates. For now, we log a warning.

langchain/vectorstores/chroma.py

@@ -28,11 +28,15 @@ class Chroma(VectorStore):
     """
 
     def __init__(
-        self, collection_name: str, embedding_function: Optional[Embeddings] = None
+        self,
+        collection_name: str,
+        embedding_function: Optional[Embeddings] = None,
+        persist_directory: Optional[str] = None,
     ) -> None:
         """Initialize with Chroma client."""
         try:
             import chromadb
+            import chromadb.config
         except ImportError:
             raise ValueError(
                 "Could not import chromadb python package. "
@@ -40,17 +44,23 @@ class Chroma(VectorStore):
             )
 
         # TODO: Add support for custom client. For now this is in-memory only.
-        self._client = chromadb.Client()
+        self._client_settings = chromadb.config.Settings()
+        if persist_directory is not None:
+            self._client_settings = chromadb.config.Settings(
+                chroma_db_impl="duckdb+parquet", persist_directory=persist_directory
+            )
+        self._client = chromadb.Client(self._client_settings)
         self._embedding_function = embedding_function
+        self._persist_directory = persist_directory
 
         # Check if the collection exists, create it if not
         if collection_name in [col.name for col in self._client.list_collections()]:
             self._collection = self._client.get_collection(name=collection_name)
-            if embedding_function is not None:
-                logger.warning(
-                    f"Collection {collection_name} already exists,"
-                    " embedding function will not be updated."
-                )
+            # TODO: Persist the user's embedding function
+            logger.warning(
+                f"Collection {collection_name} already exists,"
+                " Do you have the right embedding function?"
+            )
         else:
             self._collection = self._client.create_collection(
                 name=collection_name,
@@ -78,7 +88,12 @@ class Chroma(VectorStore):
         # TODO: Handle the case where the user doesn't provide ids on the Collection
         if ids is None:
             ids = [str(uuid.uuid1()) for _ in texts]
-        self._collection.add(metadatas=metadatas, documents=texts, ids=ids)
+        embeddings = None
+        if self._embedding_function is not None:
+            embeddings = self._embedding_function.embed_documents(list(texts))
+        self._collection.add(
+            metadatas=metadatas, embeddings=embeddings, documents=texts, ids=ids
+        )
         return ids
 
     def similarity_search(
@@ -116,6 +131,23 @@ class Chroma(VectorStore):
         ]
         return docs
 
+    def delete_collection(self) -> None:
+        """Delete the collection."""
+        self._client.delete_collection(self._collection.name)
+
+    def persist(self) -> None:
+        """Persist the collection.
+
+        This can be used to explicitly persist the data to disk.
+        It will also be called automatically when the object is destroyed.
+        """
+        if self._persist_directory is None:
+            raise ValueError(
+                "You must specify a persist_directory on"
+                "creation to persist the collection."
+            )
+        self._client.persist()
+
     @classmethod
     def from_texts(
         cls,
@@ -124,12 +156,17 @@ class Chroma(VectorStore):
         metadatas: Optional[List[dict]] = None,
         ids: Optional[List[str]] = None,
         collection_name: str = "langchain",
+        persist_directory: Optional[str] = None,
         **kwargs: Any,
     ) -> Chroma:
         """Create a Chroma vectorstore from a raw documents.
 
+        If a persist_directory is specified, the collection will be persisted there.
+        Otherwise, the data will be ephemeral in-memory.
+
         Args:
             collection_name (str): Name of the collection to create.
+            persist_directory (Optional[str]): Directory to persist the collection.
             documents (List[Document]): List of documents to add.
             embedding (Optional[Embeddings]): Embedding function. Defaults to None.
             metadatas (Optional[List[dict]]): List of metadatas. Defaults to None.
@@ -139,7 +176,9 @@ class Chroma(VectorStore):
             Chroma: Chroma vectorstore.
         """
         chroma_collection = cls(
-            collection_name=collection_name, embedding_function=embedding
+            collection_name=collection_name,
+            embedding_function=embedding,
+            persist_directory=persist_directory,
         )
         chroma_collection.add_texts(texts=texts, metadatas=metadatas, ids=ids)
         return chroma_collection
@@ -151,12 +190,17 @@ class Chroma(VectorStore):
         embedding: Optional[Embeddings] = None,
         ids: Optional[List[str]] = None,
         collection_name: str = "langchain",
+        persist_directory: Optional[str] = None,
         **kwargs: Any,
     ) -> Chroma:
         """Create a Chroma vectorstore from a list of documents.
 
+        If a persist_directory is specified, the collection will be persisted there.
+        Otherwise, the data will be ephemeral in-memory.
+
         Args:
             collection_name (str): Name of the collection to create.
+            persist_directory (Optional[str]): Directory to persist the collection.
             documents (List[Document]): List of documents to add to the vectorstore.
             embedding (Optional[Embeddings]): Embedding function. Defaults to None.
 
@@ -166,9 +210,10 @@ class Chroma(VectorStore):
         texts = [doc.page_content for doc in documents]
         metadatas = [doc.metadata for doc in documents]
         return cls.from_texts(
-            collection_name=collection_name,
             texts=texts,
             embedding=embedding,
             metadatas=metadatas,
             ids=ids,
+            collection_name=collection_name,
+            persist_directory=persist_directory,
         )

tests/integration_tests/vectorstores/test_chroma.py

@@ -26,3 +26,36 @@ def test_chroma_with_metadatas() -> None:
     )
     output = docsearch.similarity_search("foo", k=1)
     assert output == [Document(page_content="foo", metadata={"page": "0"})]
+
+
+def test_chroma_with_persistence() -> None:
+    """Test end to end construction and search, with persistence."""
+    chroma_persist_dir = "./tests/persist_dir"
+    collection_name = "test_collection"
+    texts = ["foo", "bar", "baz"]
+    docsearch = Chroma.from_texts(
+        collection_name=collection_name,
+        texts=texts,
+        embedding=FakeEmbeddings(),
+        persist_directory=chroma_persist_dir,
+    )
+
+    output = docsearch.similarity_search("foo", k=1)
+    assert output == [Document(page_content="foo")]
+
+    docsearch.persist()
+
+    # Get a new VectorStore from the persisted directory
+    docsearch = Chroma(
+        collection_name=collection_name,
+        embedding_function=FakeEmbeddings(),
+        persist_directory=chroma_persist_dir,
+    )
+    output = docsearch.similarity_search("foo", k=1)
+
+    # Clean up
+    docsearch.delete_collection()
+
+    # Persist doesn't need to be called again
+    # Data will be automatically persisted on object deletion
+    # Or on program exit