Fix/query expander duplicate queries (#12035)

haystack/components/query/query_expander.py

@@ -228,7 +228,7 @@ class QueryExpander:
                 )
                 expanded_queries = expanded_queries[:expansion_count]
 
-            # Add original query if requested and remove duplicates
+            # Add original query if not already present
             if self.include_original_query:
                 expanded_queries_lower = [q.lower() for q in expanded_queries]
                 if query.lower() not in expanded_queries_lower:
@@ -297,7 +297,7 @@ class QueryExpander:
                 )
                 expanded_queries = expanded_queries[:expansion_count]
 
-            # Add original query if requested and remove duplicates
+            # Add original query if not already present
             if self.include_original_query:
                 expanded_queries_lower = [q.lower() for q in expanded_queries]
                 if query.lower() not in expanded_queries_lower:
@@ -349,7 +349,7 @@ class QueryExpander:
         Parse the generator response to extract individual expanded queries.
 
         :param generator_response: The raw text response from the generator.
-        :return: List of parsed expanded queries.
+        :return: List of parsed expanded queries, deduplicated in first-seen order.
         """
         parsed = _parse_dict_from_json(generator_response, expected_keys=["queries"], raise_on_failure=False)
 
@@ -364,9 +364,13 @@ class QueryExpander:
             return []
 
         queries = []
+        seen: set[str] = set()
         for item in parsed["queries"]:
             if isinstance(item, str) and item.strip():
-                queries.append(item.strip())
+                stripped = item.strip()
+                if stripped not in seen:
+                    seen.add(stripped)
+                    queries.append(stripped)
             else:
                 logger.warning("Skipping non-string or empty query in response: {item}", item=item)
 

releasenotes/notes/fix-query-expander-duplicate-queries-ac349e56197b2f16.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixed ``QueryExpander`` returning duplicate queries when the chat generator repeats an
+    expansion. Generated queries are now deduplicated while preserving first-seen order,
+    so repeated expansions no longer trigger redundant retrievals or consume the requested
+    expansion budget. Both ``run`` and ``run_async`` are affected.

test/components/query/test_query_expander.py

@@ -200,6 +200,18 @@ class TestQueryExpander:
         assert result["queries"] == ["original query", "alt1", "alt2"]
         assert len(result["queries"]) == 3
 
+    def test_run_deduplicates_generated_queries(self):
+        chat_generator = MockChatGenerator('{"queries": ["same query", "same query", "other query"]}')
+        expander = QueryExpander(chat_generator=chat_generator, n_expansions=3, include_original_query=False)
+        result = expander.run("topic")
+        assert result["queries"] == ["same query", "other query"]
+
+    def test_run_deduplicates_before_truncating(self):
+        chat_generator = MockChatGenerator('{"queries": ["a", "a", "b", "c"]}')
+        expander = QueryExpander(chat_generator=chat_generator, n_expansions=3, include_original_query=False)
+        result = expander.run("topic")
+        assert result["queries"] == ["a", "b", "c"]
+
     def test_run_truncates_excess_queries(self, caplog):
         chat_generator = MockChatGenerator('{"queries": ["q1", "q2", "q3", "q4", "q5"]}')
         expander = QueryExpander(chat_generator=chat_generator, n_expansions=3, include_original_query=False)
@@ -397,6 +409,20 @@ class TestQueryExpanderAsync:
         ]
         fake_chat_generator.run.assert_called_once()
 
+    @pytest.mark.asyncio
+    async def test_run_async_deduplicates_generated_queries(self):
+        chat_generator = MockChatGenerator('{"queries": ["same query", "same query", "other query"]}')
+        expander = QueryExpander(chat_generator=chat_generator, n_expansions=3, include_original_query=False)
+        result = await expander.run_async("topic")
+        assert result["queries"] == ["same query", "other query"]
+
+    @pytest.mark.asyncio
+    async def test_run_async_deduplicates_before_truncating(self):
+        chat_generator = MockChatGenerator('{"queries": ["a", "a", "b", "c"]}')
+        expander = QueryExpander(chat_generator=chat_generator, n_expansions=3, include_original_query=False)
+        result = await expander.run_async("topic")
+        assert result["queries"] == ["a", "b", "c"]
+
 
 @pytest.mark.integration
 class TestQueryExpanderIntegration: