community: Chroma Adding create_collection_if_not_exists flag to Chroma constructor (#21420)

- **Description:** Adds the ability to either `get_or_create` or simply
`get_collection`. This is useful when dealing with read-only Chroma
instances where users are constraint to using `get_collection`. Targeted
at Http/CloudClients mostly.
- **Issue:** chroma-core/chroma#2163
- **Dependencies:** N/A
- **Twitter handle:** `@t_azarov`




| Collection Exists | create_collection_if_not_exists | Outcome | test |

|-------------------|---------------------------------|----------------------------------------------------------------|----------------------------------------------------------|
| True | False | No errors, collection state unchanged |
`test_create_collection_if_not_exist_false_existing` |
| True | True | No errors, collection state unchanged |
`test_create_collection_if_not_exist_true_existing` |
| False | False | Error, `get_collection()` fails |
`test_create_collection_if_not_exist_false_non_existing` |
| False | True | No errors, `get_or_create_collection()` creates the
collection | `test_create_collection_if_not_exist_true_non_existing` |

libs/partners/chroma/langchain_chroma/vectorstores.py

@@ -60,7 +60,8 @@ def cosine_similarity(X: Matrix, Y: Matrix) -> np.ndarray:
     Y = np.array(Y)
     if X.shape[1] != Y.shape[1]:
         raise ValueError(
-            f"Number of columns in X and Y must be the same. X has shape {X.shape} "
+            "Number of columns in X and Y must be the same. X has shape"
+            f"{X.shape} "
             f"and Y has shape {Y.shape}."
         )
 
@@ -133,6 +134,7 @@ class Chroma(VectorStore):
         collection_metadata: Optional[Dict] = None,
         client: Optional[chromadb.ClientAPI] = None,
         relevance_score_fn: Optional[Callable[[float], float]] = None,
+        create_collection_if_not_exists: Optional[bool] = True,
     ) -> None:
         """Initialize with a Chroma client."""
 
@@ -161,11 +163,14 @@ class Chroma(VectorStore):
             )
 
         self._embedding_function = embedding_function
-        self._collection = self._client.get_or_create_collection(
-            name=collection_name,
-            embedding_function=None,
-            metadata=collection_metadata,
-        )
+        if create_collection_if_not_exists:
+            self._collection = self._client.get_or_create_collection(
+                name=collection_name,
+                embedding_function=None,
+                metadata=collection_metadata,
+            )
+        else:
+            self._collection = self._client.get_collection(name=collection_name)
         self.override_relevance_score_fn = relevance_score_fn
 
     @property
@@ -650,7 +655,8 @@ class Chroma(VectorStore):
         """
         return self.update_documents([document_id], [document])
 
-    def update_documents(self, ids: List[str], documents: List[Document]) -> None:  # type: ignore
+    # type: ignore
+    def update_documents(self, ids: List[str], documents: List[Document]) -> None:
         """Update a document in the collection.
 
         Args:

libs/partners/chroma/tests/integration_tests/test_vectorstores.py

@@ -1,10 +1,12 @@
 """Test Chroma functionality."""
 
 import uuid
+from typing import Generator
 
 import chromadb
 import pytest
 import requests
+from chromadb.api.client import SharedSystemClient
 from langchain_core.documents import Document
 from langchain_core.embeddings.fake import FakeEmbeddings as Fak
 
@@ -15,6 +17,13 @@ from tests.integration_tests.fake_embeddings import (
 )
 
 
+@pytest.fixture()
+def client() -> Generator[chromadb.ClientAPI, None, None]:
+    SharedSystemClient.clear_system_cache()
+    client = chromadb.Client(chromadb.config.Settings())
+    yield client
+
+
 def test_chroma() -> None:
     """Test end to end construction and search."""
     texts = ["foo", "bar", "baz"]
@@ -271,10 +280,7 @@ def test_chroma_with_relevance_score_custom_normalization_fn() -> None:
     ]
 
 
-def test_init_from_client() -> None:
-    import chromadb
-
-    client = chromadb.Client(chromadb.config.Settings())
+def test_init_from_client(client: chromadb.ClientAPI) -> None:
     Chroma(client=client)
 
 
@@ -414,3 +420,72 @@ def test_chroma_legacy_batching() -> None:
     )
 
     db.delete_collection()
+
+
+def test_create_collection_if_not_exist_default() -> None:
+    """Tests existing behaviour without the new create_collection_if_not_exists flag."""
+    texts = ["foo", "bar", "baz"]
+    docsearch = Chroma.from_texts(
+        collection_name="test_collection", texts=texts, embedding=FakeEmbeddings()
+    )
+    assert docsearch._client.get_collection("test_collection") is not None
+    docsearch.delete_collection()
+
+
+def test_create_collection_if_not_exist_true_existing(
+    client: chromadb.ClientAPI,
+) -> None:
+    """Tests create_collection_if_not_exists=True and collection already existing."""
+    client.create_collection("test_collection")
+    vectorstore = Chroma(
+        client=client,
+        collection_name="test_collection",
+        embedding_function=FakeEmbeddings(),
+        create_collection_if_not_exists=True,
+    )
+    assert vectorstore._client.get_collection("test_collection") is not None
+    vectorstore.delete_collection()
+
+
+def test_create_collection_if_not_exist_false_existing(
+    client: chromadb.ClientAPI,
+) -> None:
+    """Tests create_collection_if_not_exists=False and collection already existing."""
+    client.create_collection("test_collection")
+    vectorstore = Chroma(
+        client=client,
+        collection_name="test_collection",
+        embedding_function=FakeEmbeddings(),
+        create_collection_if_not_exists=False,
+    )
+    assert vectorstore._client.get_collection("test_collection") is not None
+    vectorstore.delete_collection()
+
+
+def test_create_collection_if_not_exist_false_non_existing(
+    client: chromadb.ClientAPI,
+) -> None:
+    """Tests create_collection_if_not_exists=False and collection not-existing,
+    should raise."""
+    with pytest.raises(Exception, match="does not exist"):
+        Chroma(
+            client=client,
+            collection_name="test_collection",
+            embedding_function=FakeEmbeddings(),
+            create_collection_if_not_exists=False,
+        )
+
+
+def test_create_collection_if_not_exist_true_non_existing(
+    client: chromadb.ClientAPI,
+) -> None:
+    """Tests create_collection_if_not_exists=True and collection non-existing. ."""
+    vectorstore = Chroma(
+        client=client,
+        collection_name="test_collection",
+        embedding_function=FakeEmbeddings(),
+        create_collection_if_not_exists=True,
+    )
+
+    assert vectorstore._client.get_collection("test_collection") is not None
+    vectorstore.delete_collection()