CrateDB: Vector Store -- make it work using CrateDB's vector_similarity

Before, the adapter used CrateDB's built-in `_score` field for ranking.
Now, it uses the dedicated `vector_similarity()` function to compute the
similarity between two vectors.

libs/community/langchain_community/vectorstores/cratedb/base.py

@@ -260,7 +260,7 @@ def _results_to_docs_and_scores(self, results: Any) -> List[Tuple[Document, floa
                     page_content=result.EmbeddingStore.document,
                     metadata=result.EmbeddingStore.cmetadata,
                 ),
-                result._score if self.embedding_function is not None else None,
+                result.similarity if self.embedding_function is not None else None,
             )
             for result in results
         ]
@@ -324,15 +324,22 @@ def _query_collection_multi(
             results: List[Any] = (
                 session.query(  # type: ignore[attr-defined]
                     self.EmbeddingStore,
-                    # FIXME: Using `_score` is definitively the wrong choice.
-                    #        - https://github.com/crate-workbench/langchain/issues/19
-                    #        - https://github.com/crate/crate/issues/15835
                     # TODO: Original pgvector code uses `self.distance_strategy`.
                     #       CrateDB currently only supports EUCLIDEAN.
                     #       self.distance_strategy(embedding).label("distance")
-                    sqlalchemy.literal_column(
-                        f"{self.EmbeddingStore.__tablename__}._score"
-                    ).label("_score"),
+                    sqlalchemy.func.vector_similarity(
+                        self.EmbeddingStore.embedding,
+                        # TODO: Just reference the `embedding` symbol here, don't
+                        #       serialize its value prematurely.
+                        #       https://github.com/crate/crate/issues/16912
+                        #
+                        # Until that got fixed, marshal the arguments to
+                        # `vector_similarity()` manually, in order to work around
+                        # this edge case bug. We don't need to use JSON marshalling,
+                        # because Python's string representation of a list is just
+                        # right.
+                        sqlalchemy.text(str(embedding)),
+                    ).label("similarity"),
                 )
                 .filter(filter_by)
                 # CrateDB applies `KNN_MATCH` within the `WHERE` clause.
@@ -341,7 +348,7 @@ def _query_collection_multi(
                         self.EmbeddingStore.embedding, embedding, k
                     )
                 )
-                .order_by(sqlalchemy.desc("_score"))
+                .order_by(sqlalchemy.desc("similarity"))
                 .join(
                     self.CollectionStore,
                     self.EmbeddingStore.collection_id == self.CollectionStore.uuid,
@@ -450,7 +457,7 @@ def _select_relevance_score_fn(self) -> Callable[[float], float]:
             )
 
     @staticmethod
-    def _euclidean_relevance_score_fn(score: float) -> float:
+    def _euclidean_relevance_score_fn(similarity: float) -> float:
         """Return a similarity score on a scale [0, 1]."""
         # The 'correct' relevance function
         # may differ depending on a few things, including:
@@ -465,4 +472,4 @@ def _euclidean_relevance_score_fn(score: float) -> float:
 
         # Original:
         # return 1.0 - distance / math.sqrt(2)
-        return score / math.sqrt(2)
+        return similarity / math.sqrt(2)

libs/community/tests/integration_tests/vectorstores/test_cratedb.py

@@ -232,7 +232,7 @@ def test_cratedb_with_metadatas_with_scores() -> None:
         pre_delete_collection=True,
     )
     output = docsearch.similarity_search_with_score("foo", k=1)
-    assert output == [(Document(page_content="foo", metadata={"page": "0"}), 2.0)]
+    assert output == [(Document(page_content="foo", metadata={"page": "0"}), 1.0)]
 
 
 def test_cratedb_with_filter_match() -> None:
@@ -250,9 +250,7 @@ def test_cratedb_with_filter_match() -> None:
     # TODO: Original:
     #       assert output == [(Document(page_content="foo", metadata={"page": "0"}), 0.0)]  # noqa: E501
     output = docsearch.similarity_search_with_score("foo", k=1, filter={"page": "0"})
-    assert output == [
-        (Document(page_content="foo", metadata={"page": "0"}), pytest.approx(2.2, 0.3))
-    ]
+    assert output == [(Document(page_content="foo", metadata={"page": "0"}), 1.0)]
 
 
 def test_cratedb_with_filter_distant_match() -> None:
@@ -269,9 +267,7 @@ def test_cratedb_with_filter_distant_match() -> None:
     )
     output = docsearch.similarity_search_with_score("foo", k=2, filter={"page": "2"})
     # Original score value: 0.0013003906671379406
-    assert output == [
-        (Document(page_content="baz", metadata={"page": "2"}), pytest.approx(1.5, 0.2))
-    ]
+    assert output == [(Document(page_content="baz", metadata={"page": "2"}), 0.2)]
 
 
 def test_cratedb_with_filter_no_match() -> None:
@@ -425,8 +421,8 @@ def test_cratedb_with_filter_in_set() -> None:
     )
     # Original score values: 0.0, 0.0013003906671379406
     assert output == [
-        (Document(page_content="foo", metadata={"page": "0"}), pytest.approx(3.0, 0.1)),
-        (Document(page_content="baz", metadata={"page": "2"}), pytest.approx(2.2, 0.1)),
+        (Document(page_content="foo", metadata={"page": "0"}), 1.0),
+        (Document(page_content="baz", metadata={"page": "2"}), 0.2),
     ]
 
 
@@ -474,9 +470,9 @@ def test_cratedb_relevance_score() -> None:
     output = docsearch.similarity_search_with_relevance_scores("foo", k=3)
     # Original score values: 1.0, 0.9996744261675065, 0.9986996093328621
     assert output == [
-        (Document(page_content="foo", metadata={"page": "0"}), pytest.approx(1.4, 0.1)),
-        (Document(page_content="bar", metadata={"page": "1"}), pytest.approx(1.1, 0.1)),
-        (Document(page_content="baz", metadata={"page": "2"}), pytest.approx(0.8, 0.1)),
+        (Document(page_content="foo", metadata={"page": "0"}), 0.7071067811865475),
+        (Document(page_content="bar", metadata={"page": "1"}), 0.35355339059327373),
+        (Document(page_content="baz", metadata={"page": "2"}), 0.1414213562373095),
     ]
 
 
@@ -495,9 +491,9 @@ def test_cratedb_retriever_search_threshold() -> None:
 
     retriever = docsearch.as_retriever(
         search_type="similarity_score_threshold",
-        search_kwargs={"k": 3, "score_threshold": 0.999},
+        search_kwargs={"k": 3, "score_threshold": 0.35},  # Original value: 0.999
     )
-    output = retriever.get_relevant_documents("summer")
+    output = retriever.invoke("summer")
     assert output == [
         Document(page_content="foo", metadata={"page": "0"}),
         Document(page_content="bar", metadata={"page": "1"}),
@@ -522,7 +518,7 @@ def test_cratedb_retriever_search_threshold_custom_normalization_fn() -> None:
         search_type="similarity_score_threshold",
         search_kwargs={"k": 3, "score_threshold": 0.5},
     )
-    output = retriever.get_relevant_documents("foo")
+    output = retriever.invoke("foo")
     assert output == []
 
 
@@ -551,7 +547,7 @@ def test_cratedb_max_marginal_relevance_search_with_score() -> None:
         pre_delete_collection=True,
     )
     output = docsearch.max_marginal_relevance_search_with_score("foo", k=1, fetch_k=3)
-    assert output == [(Document(page_content="foo"), 2.0)]
+    assert output == [(Document(page_content="foo"), 1.0)]
 
 
 def test_cratedb_multicollection_search_success() -> None: