add rerank() command to the ES|QL query builder

elasticsearch/esql/esql.py

@@ -143,7 +143,7 @@ def _is_forked(self) -> bool:
         return False
 
     def change_point(self, value: FieldType) -> "ChangePoint":
-        """`CHANGE_POINT` detects spikes, dips, and change points in a metric.
+        """``CHANGE_POINT`` detects spikes, dips, and change points in a metric.
 
         :param value: The column with the metric in which you want to detect a change point.
 
@@ -163,17 +163,18 @@ def change_point(self, value: FieldType) -> "ChangePoint":
     def completion(
         self, *prompt: ExpressionType, **named_prompt: ExpressionType
     ) -> "Completion":
-        """The `COMPLETION` command allows you to send prompts and context to a Large
+        """The ``COMPLETION`` command allows you to send prompts and context to a Large
         Language Model (LLM) directly within your ES|QL queries, to perform text
         generation tasks.
 
         :param prompt: The input text or expression used to prompt the LLM. This can
                        be a string literal or a reference to a column containing text.
         :param named_prompt: The input text or expresion, given as a keyword argument.
-                             The argument name is used for the column name. If not
-                             specified, the results will be stored in a column named
-                             `completion`. If the specified column already exists, it
-                             will be overwritten with the new results.
+                             The argument name is used for the column name. If the
+                             prompt is given as a positional argument, the results will
+                             be stored in a column named ``completion``. If the
+                             specified column already exists, it will be overwritten
+                             with the new results.
 
         Examples::
 
@@ -439,6 +440,54 @@ def rename(self, **columns: FieldType) -> "Rename":
         """
         return Rename(self, **columns)
 
+    def rerank(self, *query: ExpressionType, **named_query: ExpressionType) -> "Rerank":
+        """The ``RERANK`` command uses an inference model to compute a new relevance score
+        for an initial set of documents, directly within your ES|QL queries.
+
+        :param query: The query text used to rerank the documents. This is typically the
+                      same query used in the initial search.
+        :param named_query: The query text used to rerank the documents, given as a
+                            keyword argument. The argument name is used for the column
+                            name. If the query is given as a positional argument, the
+                            results will be stored in a column named `_score`. If the
+                            specified column already exists, it will be overwritten with
+                            the new results.
+
+        Examples::
+
+            query1 = (
+                ESQL.from_("books").metadata("_score")
+                .where('MATCH(description, "hobbit")')
+                .sort("_score DESC")
+                .limit(100)
+                .rerank("hobbit").on("description").with_(inference_id="test_reranker")
+                .limit(3)
+                .keep("title", "_score")
+            )
+            query2 = (
+                ESQL.from_("books").metadata("_score")
+                .where('MATCH(description, "hobbit") OR MATCH(author, "Tolkien")')
+                .sort("_score DESC")
+                .limit(100)
+                .rerank(rerank_score="hobbit").on("description", "author").with_(inference_id="test_reranker")
+                .sort("rerank_score")
+                .limit(3)
+                .keep("title", "_score", "rerank_score")
+            )
+            query3 = (
+                ESQL.from_("books").metadata("_score")
+                .where('MATCH(description, "hobbit") OR MATCH(author, "Tolkien")')
+                .sort("_score DESC")
+                .limit(100)
+                .rerank(rerank_score="hobbit").on("description", "author").with_(inference_id="test_reranker")
+                .eval(original_score="_score", _score="rerank_score + original_score")
+                .sort("_score")
+                .limit(3)
+                .keep("title", "original_score", "rerank_score", "_score")
+            )
+        """
+        return Rerank(self, *query, **named_query)
+
     def sample(self, probability: float) -> "Sample":
         """The ``SAMPLE`` command samples a fraction of the table rows.
 
@@ -1046,6 +1095,65 @@ def _render_internal(self) -> str:
         return f'RENAME {", ".join([f"{self._format_id(old_name)} AS {self._format_id(new_name)}" for old_name, new_name in self._columns.items()])}'
 
 
+class Rerank(ESQLBase):
+    """Implementation of the ``RERANK`` processing command.
+
+    This class inherits from :class:`ESQLBase <elasticsearch.esql.esql.ESQLBase>`,
+    to make it possible to chain all the commands that belong to an ES|QL query
+    in a single expression.
+    """
+
+    def __init__(
+        self, parent: ESQLBase, *query: ExpressionType, **named_query: ExpressionType
+    ):
+        if len(query) + len(named_query) > 1:
+            raise ValueError(
+                "this method requires either one positional or one keyword argument only"
+            )
+        super().__init__(parent)
+        self._query = query
+        self._named_query = named_query
+        self._fields: Optional[Tuple[str, ...]] = None
+        self._inference_id: Optional[str] = None
+
+    def on(self, *fields: str) -> "Rerank":
+        self._fields = fields
+        return self
+
+    def with_(self, inference_id: str) -> "Rerank":
+        """Continuation of the `COMPLETION` command.
+
+        :param inference_id: The ID of the inference endpoint to use for the task. The
+                             inference endpoint must be configured with the completion
+                             task type.
+        """
+        self._inference_id = inference_id
+        return self
+
+    def _render_internal(self) -> str:
+        if self._fields is None:
+            raise ValueError(
+                "The rerank command requires one or more fields to rerank on"
+            )
+        if self._inference_id is None:
+            raise ValueError("The completion command requires an inference ID")
+        with_ = {"inference_id": self._inference_id}
+        if self._named_query:
+            column = list(self._named_query.keys())[0]
+            query = list(self._named_query.values())[0]
+            return (
+                f"RERANK {self._format_id(column)} = {json.dumps(query)} "
+                f"ON {', '.join([self._format_id(field) for field in self._fields])} "
+                f"WITH {json.dumps(with_)}"
+            )
+        else:
+            return (
+                f"RERANK {json.dumps(self._query[0])} "
+                f"ON {', '.join([self._format_id(field) for field in self._fields])} "
+                f"WITH {json.dumps(with_)}"
+            )
+
+
 class Sample(ESQLBase):
     """Implementation of the ``SAMPLE`` processing command.
 

test_elasticsearch/test_esql.py

@@ -422,6 +422,83 @@ def test_rename():
     )
 
 
+def test_rerank():
+    query = (
+        ESQL.from_("books")
+        .metadata("_score")
+        .where('MATCH(description, "hobbit")')
+        .sort("_score DESC")
+        .limit(100)
+        .rerank("hobbit")
+        .on("description")
+        .with_(inference_id="test_reranker")
+        .limit(3)
+        .keep("title", "_score")
+    )
+    assert (
+        query.render()
+        == """FROM books METADATA _score
+| WHERE MATCH(description, "hobbit")
+| SORT _score DESC
+| LIMIT 100
+| RERANK "hobbit" ON description WITH {"inference_id": "test_reranker"}
+| LIMIT 3
+| KEEP title, _score"""
+    )
+
+    query = (
+        ESQL.from_("books")
+        .metadata("_score")
+        .where('MATCH(description, "hobbit") OR MATCH(author, "Tolkien")')
+        .sort("_score DESC")
+        .limit(100)
+        .rerank(rerank_score="hobbit")
+        .on("description", "author")
+        .with_(inference_id="test_reranker")
+        .sort("rerank_score")
+        .limit(3)
+        .keep("title", "_score", "rerank_score")
+    )
+    assert (
+        query.render()
+        == """FROM books METADATA _score
+| WHERE MATCH(description, "hobbit") OR MATCH(author, "Tolkien")
+| SORT _score DESC
+| LIMIT 100
+| RERANK rerank_score = "hobbit" ON description, author WITH {"inference_id": "test_reranker"}
+| SORT rerank_score
+| LIMIT 3
+| KEEP title, _score, rerank_score"""
+    )
+
+    query = (
+        ESQL.from_("books")
+        .metadata("_score")
+        .where('MATCH(description, "hobbit") OR MATCH(author, "Tolkien")')
+        .sort("_score DESC")
+        .limit(100)
+        .rerank(rerank_score="hobbit")
+        .on("description", "author")
+        .with_(inference_id="test_reranker")
+        .eval(original_score="_score", _score="rerank_score + original_score")
+        .sort("_score")
+        .limit(3)
+        .keep("title", "original_score", "rerank_score", "_score")
+    )
+    assert (
+        query.render()
+        == """FROM books METADATA _score
+| WHERE MATCH(description, "hobbit") OR MATCH(author, "Tolkien")
+| SORT _score DESC
+| LIMIT 100
+| RERANK rerank_score = "hobbit" ON description, author WITH {"inference_id": "test_reranker"}
+| EVAL original_score = _score, _score = rerank_score + original_score
+| SORT _score
+| LIMIT 3
+| KEEP title, original_score, rerank_score, _score"""
+    )
+
+
 def test_sample():
     query = ESQL.from_("employees").keep("emp_no").sample(0.05)
     assert (