Add knn and query search field options to ElasticKnnSearch (#5641)

in the `ElasticKnnSearch` class added 2 arguments that were not exposed
properly

`knn_search` added:
- `vector_query_field: Optional[str] = 'vector'`
-- vector_query_field: Field name to use in knn search if not default
'vector'

`knn_hybrid_search` added:
- `vector_query_field: Optional[str] = 'vector'`
-- vector_query_field: Field name to use in knn search if not default
'vector'
- `query_field: Optional[str] = 'text'`
-- query_field: Field name to use in search if not default 'text'



Fixes # https://github.com/hwchase17/langchain/issues/5633


cc: @dev2049 @hwchase17

---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

langchain/vectorstores/elastic_vector_search.py

@@ -334,6 +334,8 @@ class ElasticKnnSearch(ElasticVectorSearch):
         es_cloud_id: Optional[str] = None,
         es_user: Optional[str] = None,
         es_password: Optional[str] = None,
+        vector_query_field: Optional[str] = "vector",
+        query_field: Optional[str] = "text",
     ):
         """
         Initializes an instance of the ElasticKnnSearch class and sets up the
@@ -362,6 +364,8 @@ class ElasticKnnSearch(ElasticVectorSearch):
 
         self.embedding = embedding
         self.index_name = index_name
+        self.query_field = query_field
+        self.vector_query_field = vector_query_field
 
         # If a pre-existing Elasticsearch connection is provided, use it.
         if es_connection is not None:
@@ -394,17 +398,16 @@ class ElasticKnnSearch(ElasticVectorSearch):
             }
         }
 
-    @staticmethod
     def _default_knn_query(
+        self,
         query_vector: Optional[List[float]] = None,
         query: Optional[str] = None,
         model_id: Optional[str] = None,
-        field: Optional[str] = "vector",
         k: Optional[int] = 10,
         num_candidates: Optional[int] = 10,
     ) -> Dict:
         knn: Dict = {
-            "field": field,
+            "field": self.vector_query_field,
             "k": k,
             "num_candidates": num_candidates,
         }
@@ -462,6 +465,7 @@ class ElasticKnnSearch(ElasticVectorSearch):
             source: Whether to include the source of each hit in the results.
             fields: The fields to include in the source of each hit. If None, all
                 fields are included.
+            vector_query_field: Field name to use in knn search if not default 'vector'
 
         Returns:
             The search results.
@@ -524,6 +528,8 @@ class ElasticKnnSearch(ElasticVectorSearch):
             fields
                 The fields to include in the source of each hit. If None, all fields are
                 included. Defaults to None.
+            vector_query_field: Field name to use in knn search if not default 'vector'
+            query_field: Field name to use in search if not default 'text'
 
         Returns:
             The search results.
@@ -541,7 +547,9 @@ class ElasticKnnSearch(ElasticVectorSearch):
         knn_query_body["boost"] = knn_boost
 
         # Generate the body of the standard Elasticsearch query
-        match_query_body = {"match": {"text": {"query": query, "boost": query_boost}}}
+        match_query_body = {
+            "match": {self.query_field: {"query": query, "boost": query_boost}}
+        }
 
         # Perform the hybrid search on the Elasticsearch index and return the results.
         res = self.client.search(