Refactor Cypher query string for linear ranker

Author: willtai

src/neo4j_graphrag/neo4j_queries.py

@@ -198,20 +198,15 @@ def _get_hybrid_query_linear(neo4j_version_is_5_23_or_above: bool, alpha: float)
         f"{NODE_VECTOR_INDEX_QUERY} "
         "WITH collect({node: node, score: score}) AS nodes, max(score) AS vector_index_max_score "
         "UNWIND nodes AS n "
-        "RETURN n.node AS node, (n.score / vector_index_max_score) AS score, 'vector' AS source "
+        "WITH n.node AS node, (n.score / vector_index_max_score) AS rawScore "
+        "RETURN node, rawScore * $alpha AS score "
         "UNION "
         f"{FULL_TEXT_SEARCH_QUERY} "
         "WITH collect({node: node, score: score}) AS nodes, max(score) AS ft_index_max_score "
         "UNWIND nodes AS n "
-        "RETURN n.node AS node, (n.score / ft_index_max_score) AS score, 'ft' AS source } "
-        "WITH node, "
-        "sum(CASE WHEN source = 'vector' THEN score * "
-        + "$alpha "
-        + " ELSE 0 END) + "
-        + "sum(CASE WHEN source = 'ft' THEN score * "
-        + "(1 - $alpha) "
-        + " ELSE 0 END) AS score "
-        "ORDER BY score DESC LIMIT $top_k"
+        "WITH n.node AS node, (n.score / ft_index_max_score) AS rawScore "
+        "RETURN node, rawScore * (1 - $alpha) AS score } "
+        "WITH node, sum(score) AS score ORDER BY score DESC LIMIT $top_k"
     )
     return call_prefix + query_body
 

tests/unit/test_neo4j_queries.py

@@ -256,8 +256,8 @@ def test_get_query_tail_ordering_no_retrieval_query() -> None:
 
 def test_get_hybrid_query_linear_with_alpha() -> None:
     query = _get_hybrid_query_linear(neo4j_version_is_5_23_or_above=True, alpha=0.7)
-    vector_substr = "CASE WHEN source = 'vector' THEN score * $alpha"
-    ft_substr = "CASE WHEN source = 'ft' THEN score * (1 - $alpha)"
+    vector_substr = "rawScore * $alpha"
+    ft_substr = "rawScore * (1 - $alpha)"
     assert vector_substr in query
     assert ft_substr in query