Fix filter expression being overridden with blank string (redis#375)

passing a string as filter expression no longer sets the filter to a blank string

Author: justin-cechmanek

redisvl/query/aggregate.py

@@ -210,10 +210,9 @@ def _tokenize_and_escape_query(self, user_query: str) -> str:
 
     def _build_query_string(self) -> str:
         """Build the full query string for text search with optional filtering."""
+        filter_expression = self._filter_expression
         if isinstance(self._filter_expression, FilterExpression):
             filter_expression = str(self._filter_expression)
-        else:
-            filter_expression = ""
 
         # base KNN query
         knn_query = f"KNN {self._num_results} @{self._vector_field} ${self.VECTOR_PARAM} AS {self.DISTANCE_ID}"
@@ -224,3 +223,7 @@ def _build_query_string(self) -> str:
             text += f" AND {filter_expression}"
 
         return f"{text})=>[{knn_query}]"
+
+    def __str__(self) -> str:
+        """Return the string representation of the query."""
+        return " ".join([str(x) for x in self.build_args()])

tests/unit/test_aggregation_types.py

@@ -113,3 +113,80 @@ def test_aggregate_hybrid_query():
             vector_field_name,
             stopwords=[1, 2, 3],
         )
+
+
+def test_hybrid_query_with_string_filter():
+    """Test that HybridQuery correctly includes string filter expressions in query string.
+
+    This test ensures that when a string filter expression is passed to HybridQuery,
+    it's properly included in the generated query string and not set to empty.
+    Regression test for bug where string filters were being ignored.
+    """
+    text = "search for document 12345"
+    text_field_name = "description"
+    vector_field_name = "embedding"
+
+    # Test with string filter expression - should include filter in query string
+    string_filter = "@category:{tech|science|engineering}"
+    hybrid_query = HybridQuery(
+        text=text,
+        text_field_name=text_field_name,
+        vector=sample_vector,
+        vector_field_name=vector_field_name,
+        filter_expression=string_filter,
+    )
+
+    # Check that filter is stored correctly
+    print("hybrid_query.filter ===", hybrid_query.filter)
+    assert hybrid_query._filter_expression == string_filter
+
+    # Check that the generated query string includes both text search and filter
+    query_string = str(hybrid_query)
+    assert f"@{text_field_name}:(search | document | 12345)" in query_string
+    assert f"AND {string_filter}" in query_string
+
+    # Test with FilterExpression - should also work (existing functionality)
+    filter_expression = Tag("category") == "tech"
+    hybrid_query_with_filter_expr = HybridQuery(
+        text=text,
+        text_field_name=text_field_name,
+        vector=sample_vector,
+        vector_field_name=vector_field_name,
+        filter_expression=filter_expression,
+    )
+
+    # Check that filter is stored correctly
+    assert hybrid_query_with_filter_expr._filter_expression == filter_expression
+
+    # Check that the generated query string includes both text search and filter
+    query_string_with_filter_expr = str(hybrid_query_with_filter_expr)
+    assert (
+        f"@{text_field_name}:(search | document | 12345)"
+        in query_string_with_filter_expr
+    )
+    assert "AND @category:{tech}" in query_string_with_filter_expr
+
+    # Test with no filter - should only have text search
+    hybrid_query_no_filter = HybridQuery(
+        text=text,
+        text_field_name=text_field_name,
+        vector=sample_vector,
+        vector_field_name=vector_field_name,
+    )
+
+    query_string_no_filter = str(hybrid_query_no_filter)
+    assert f"@{text_field_name}:(search | document | 12345)" in query_string_no_filter
+    assert "AND" not in query_string_no_filter
+
+    # Test with wildcard filter - should only have text search (no AND clause)
+    hybrid_query_wildcard = HybridQuery(
+        text=text,
+        text_field_name=text_field_name,
+        vector=sample_vector,
+        vector_field_name=vector_field_name,
+        filter_expression="*",
+    )
+
+    query_string_wildcard = str(hybrid_query_wildcard)
+    assert f"@{text_field_name}:(search | document | 12345)" in query_string_wildcard
+    assert "AND" not in query_string_wildcard

tests/unit/test_query_types.py

@@ -305,7 +305,6 @@ def test_text_query_with_string_filter():
     query_string = str(text_query)
     assert f"@{text_field_name}:(search | document | 12345)" in query_string
     assert f"AND {string_filter}" in query_string
-    assert string_filter in query_string
 
     # Test with FilterExpression - should also work (existing functionality)
     filter_expression = Tag("category") == "tech"