[Backport 8.x] Add rank option to elasticsearch_dsl.search.Search

elasticsearch_dsl/search.py

@@ -318,8 +318,9 @@ def __init__(self, **kwargs):
 
         self.aggs = AggsProxy(self)
         self._sort = []
-        self._collapse = {}
         self._knn = []
+        self._rank = {}
+        self._collapse = {}
         self._source = None
         self._highlight = {}
         self._highlight_opts = {}
@@ -408,6 +409,7 @@ def _clone(self):
 
         s._response_class = self._response_class
         s._knn = [knn.copy() for knn in self._knn]
+        s._rank = self._rank.copy()
         s._collapse = self._collapse.copy()
         s._sort = self._sort[:]
         s._source = copy.copy(self._source) if self._source is not None else None
@@ -451,6 +453,8 @@ def update_from_dict(self, d):
             self._knn = d.pop("knn")
             if isinstance(self._knn, dict):
                 self._knn = [self._knn]
+        if "rank" in d:
+            self._rank = d.pop("rank")
         if "collapse" in d:
             self._collapse = d.pop("collapse")
         if "sort" in d:
@@ -558,6 +562,27 @@ def knn(
             s._knn[-1]["similarity"] = similarity
         return s
 
+    def rank(self, rrf=None):
+        """
+        Defines a method for combining and ranking results sets from a combination
+        of searches. Requires a minimum of 2 results sets.
+
+        :arg rrf: Set to ``True`` or an options dictionary to set the rank method to reciprocal rank fusion (RRF).
+
+        Example::
+            s = Search()
+            s = s.query('match', content='search text')
+            s = s.knn(field='embedding', k=5, num_candidates=10, query_vector=vector)
+            s = s.rank(rrf=True)
+
+        Note: This option is in technical preview and may change in the future. The syntax will likely change before GA.
+        """
+        s = self._clone()
+        s._rank = {}
+        if rrf is not None and rrf is not False:
+            s._rank["rrf"] = {} if rrf is True else rrf
+        return s
+
     def source(self, fields=None, **kwargs):
         """
         Selectively control how the _source field is returned.
@@ -747,6 +772,9 @@ def to_dict(self, count=False, **kwargs):
             else:
                 d["knn"] = self._knn
 
+        if self._rank:
+            d["rank"] = self._rank
+
         # count request doesn't care for sorting and other things
         if not count:
             if self.post_filter:

tests/test_search.py

@@ -288,6 +288,18 @@ def test_knn():
     } == s.to_dict()
 
 
+def test_rank():
+    s = search.Search()
+    s.rank(rrf=False)
+    assert {} == s.to_dict()
+
+    s = s.rank(rrf=True)
+    assert {"rank": {"rrf": {}}} == s.to_dict()
+
+    s = s.rank(rrf={"window_size": 50, "rank_constant": 20})
+    assert {"rank": {"rrf": {"window_size": 50, "rank_constant": 20}}} == s.to_dict()
+
+
 def test_sort():
     s = search.Search()
     s = s.sort("fielda", "-fieldb")