Add fuzziness support in Elasticsearch bm25 retrieval

document_stores/elasticsearch/src/elasticsearch_haystack/bm25_retriever.py

@@ -16,6 +16,7 @@ def __init__(
         *,
         document_store: ElasticsearchDocumentStore,
         filters: Optional[Dict[str, Any]] = None,
+        fuzziness: str = "AUTO",
         top_k: int = 10,
         scale_score: bool = True,
     ):
@@ -25,13 +26,15 @@ def __init__(
 
         self._document_store = document_store
         self._filters = filters or {}
+        self._fuzziness = fuzziness
         self._top_k = top_k
         self._scale_score = scale_score
 
     def to_dict(self) -> Dict[str, Any]:
         return default_to_dict(
             self,
             filters=self._filters,
+            fuzziness=self._fuzziness,
             top_k=self._top_k,
             scale_score=self._scale_score,
             document_store=self._document_store.to_dict(),
@@ -47,6 +50,10 @@ def from_dict(cls, data: Dict[str, Any]) -> "ElasticsearchBM25Retriever":
     @component.output_types(documents=List[Document])
     def run(self, query: str):
         docs = self._document_store._bm25_retrieval(
-            query=query, filters=self._filters, top_k=self._top_k, scale_score=self._scale_score
+            query=query,
+            filters=self._filters,
+            fuzziness=self._fuzziness,
+            top_k=self._top_k,
+            scale_score=self._scale_score,
         )
         return {"documents": docs}

document_stores/elasticsearch/src/elasticsearch_haystack/document_store.py

@@ -246,6 +246,7 @@ def _bm25_retrieval(
         query: str,
         *,
         filters: Optional[Dict[str, Any]] = None,
+        fuzziness: str = "AUTO",
         top_k: int = 10,
         scale_score: bool = True,
     ) -> List[Document]:
@@ -263,6 +264,9 @@ def _bm25_retrieval(
         :param query: String to search in saved Documents' text.
         :param filters: Filters applied to the retrieved Documents, for more info
                         see `ElasticsearchDocumentStore.filter_documents`, defaults to None
+        :param fuzziness: Fuzziness parameter passed to Elasticsearch, defaults to "AUTO".
+                          see the official documentation for valid values:
+                          https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#fuzziness
         :param top_k: Maximum number of Documents to return, defaults to 10
         :param scale_score: If `True` scales the Document`s scores between 0 and 1, defaults to True
         :raises ValueError: If `query` is an empty string
@@ -281,6 +285,7 @@ def _bm25_retrieval(
                         {
                             "multi_match": {
                                 "query": query,
+                                "fuzziness": fuzziness,
                                 "type": "most_fields",
                                 "operator": "AND",
                             }

document_stores/elasticsearch/tests/test_bm25_retriever.py

@@ -31,6 +31,7 @@ def test_to_dict(_mock_elasticsearch_client):
                 "type": "ElasticsearchDocumentStore",
             },
             "filters": {},
+            "fuzziness": "AUTO",
             "top_k": 10,
             "scale_score": True,
         },
@@ -47,13 +48,15 @@ def test_from_dict(_mock_elasticsearch_client):
                 "type": "ElasticsearchDocumentStore",
             },
             "filters": {},
+            "fuzziness": "AUTO",
             "top_k": 10,
             "scale_score": True,
         },
     }
     retriever = ElasticsearchBM25Retriever.from_dict(data)
     assert retriever._document_store
     assert retriever._filters == {}
+    assert retriever._fuzziness == "AUTO"
     assert retriever._top_k == 10
     assert retriever._scale_score
 
@@ -66,6 +69,7 @@ def test_run():
     mock_store._bm25_retrieval.assert_called_once_with(
         query="some query",
         filters={},
+        fuzziness="AUTO",
         top_k=10,
         scale_score=True,
     )

document_stores/elasticsearch/tests/test_document_store.py

@@ -82,6 +82,36 @@ def test_bm25_retrieval(self, docstore: ElasticsearchDocumentStore):
         assert "functional" in res[1].content
         assert "functional" in res[2].content
 
+    def test_bm25_retrieval_with_fuzziness(self, docstore: ElasticsearchDocumentStore):
+        docstore.write_documents(
+            [
+                Document(content="Haskell is a functional programming language"),
+                Document(content="Lisp is a functional programming language"),
+                Document(content="Exilir is a functional programming language"),
+                Document(content="F# is a functional programming language"),
+                Document(content="C# is a functional programming language"),
+                Document(content="C++ is an object oriented programming language"),
+                Document(content="Dart is an object oriented programming language"),
+                Document(content="Go is an object oriented programming language"),
+                Document(content="Python is a object oriented programming language"),
+                Document(content="Ruby is a object oriented programming language"),
+                Document(content="PHP is a object oriented programming language"),
+            ]
+        )
+
+        query_with_typo = "functinal"
+        # Query without fuzziness to search for the exact match
+        res = docstore._bm25_retrieval(query_with_typo, top_k=3, fuzziness="0")
+        # Nothing is found as the query contains a typo
+        assert res == []
+
+        # Query with fuzziness with the same query
+        res = docstore._bm25_retrieval(query_with_typo, top_k=3, fuzziness="1")
+        assert len(res) == 3
+        assert "functional" in res[0].content
+        assert "functional" in res[1].content
+        assert "functional" in res[2].content
+
     def test_write_duplicate_fail(self, docstore: ElasticsearchDocumentStore):
         """
         Verify `DuplicateDocumentError` is raised when trying to write duplicate files.