Update Cypher retrieval queries (#259)

* Update Cypher retrieval queries to handle cases where the matched node has no relationship

* Use camelCase for variable names

* Ruff

* Fix the fix

Author: stellasia

docs/source/user_guide_rag.rst

@@ -561,12 +561,9 @@ certain movie properties, the retrieval query can be structured as follows:
 .. code:: python
 
     retrieval_query = """
-        MATCH
-        (actor:Actor)-[:ACTED_IN]->(node)
-        RETURN
-        node.title AS movie_title,
-        node.plot AS movie_plot,
-        collect(actor.name) AS actors;
+    RETURN  node.title as movieTitle,
+            node.plot as moviePlot,
+            collect { MATCH (actor:Actor)-[:ACTED_IN]->(node) RETURN actor.name } AS actors
     """
     retriever = VectorCypherRetriever(
         driver,
@@ -593,8 +590,8 @@ The `content` field is a formatted string containing the key information intende
 .. code:: python
 
     def result_formatter(record: neo4j.Record) -> RetrieverResultItem:
+        content=f"Movie title: {record.get('movieTitle')}, description: {record.get('movieDescription')}, actors: {record.get('actors')}",
         return RetrieverResultItem(
-            content=f"Movie title: {record.get('movieTitle')}, description: {record.get('movieDescription')}, actors: {record.get('actors')}",
             metadata={
                 "title": record.get('movieTitle'),
                 "score": record.get("score"),
@@ -604,7 +601,7 @@ The `content` field is a formatted string containing the key information intende
     retriever = VectorCypherRetriever(
         driver,
         index_name=INDEX_NAME,
-        retrieval_query="MATCH (node)<-[:ACTED_IN]-(p:Person) RETURN node.title as movieTitle, node.plot as movieDescription, collect(p.name) as actors, score",
+        retrieval_query="OPTIONAL MATCH (node)<-[:ACTED_IN]-(p:Person) RETURN node.title as movieTitle, node.plot as movieDescription, collect(p.name) as actors, score",
         result_formatter=result_formatter,
     )
 
@@ -763,7 +760,7 @@ the graph and return more context:
         driver,
         INDEX_NAME,
         FULLTEXT_INDEX_NAME,
-        retrieval_query="MATCH (node)-[:AUTHORED_BY]->(author:Author)" "RETURN author.name"
+        retrieval_query="MATCH (node)-[:AUTHORED_BY]->(author:Author) RETURN author.name"
         embedder=embedder,
     )
 

examples/customize/retrievers/result_formatter_vector_cypher_retriever.py

@@ -21,7 +21,12 @@
 
 # for each Movie node matched by the vector search, retrieve more context:
 # the name of all actors starring in that movie
-RETRIEVAL_QUERY = " MATCH (node)<-[:ACTED_IN]-(p:Person) RETURN node.title as movieTitle, node.plot as moviePlot, collect(p.name) as actors, score as similarityScore"
+RETRIEVAL_QUERY = """
+RETURN  node.title as movieTitle,
+        node.plot as moviePlot,
+        collect { MATCH (actor:Actor)-[:ACTED_IN]->(node) RETURN actor.name } AS actors,
+        score as similarityScore
+"""
 
 
 def my_result_formatter(record: neo4j.Record) -> RetrieverResultItem:

examples/retrieve/hybrid_cypher_retriever.py

@@ -22,7 +22,12 @@
 
 # for each Movie node matched by the vector search, retrieve more context:
 # the name of all actors starring in that movie
-RETRIEVAL_QUERY = " MATCH (node)<-[:ACTED_IN]-(p:Person) RETURN node.title as movieTitle, node.plot as moviePlot, collect(p.name) as actors, score as similarityScore"
+RETRIEVAL_QUERY = """
+RETURN  node.title as movieTitle,
+        node.plot as moviePlot,
+        collect { MATCH (actor:Actor)-[:ACTED_IN]->(node) RETURN actor.name } AS actors,
+        score as similarityScore
+"""
 
 with neo4j.GraphDatabase.driver(URI, auth=AUTH) as driver:
     # Initialize the retriever

examples/retrieve/vector_cypher_retriever.py

@@ -20,7 +20,12 @@
 
 # for each Movie node matched by the vector search, retrieve more context:
 # the name of all actors starring in that movie
-RETRIEVAL_QUERY = " MATCH (node)<-[:ACTED_IN]-(p:Person) RETURN node.title as movieTitle, node.plot as moviePlot, collect(p.name) as actors, score as similarityScore"
+RETRIEVAL_QUERY = """
+RETURN  node.title as movieTitle,
+        node.plot as moviePlot,
+        collect { MATCH (actor:Actor)-[:ACTED_IN]->(node) RETURN actor.name } AS actors,
+        score as similarityScore
+"""
 
 with neo4j.GraphDatabase.driver(URI, auth=AUTH) as driver:
     # Initialize the retriever