Improve performance of NeptuneAnalyticsGraph (#311)

Improved the graph schema retrieval performance of
`NeptuneAnalyticsGraph` by using the
[pg_schema](https://docs.aws.amazon.com/neptune-analytics/latest/userguide/custom-algorithms-property-graph-schema.html)
algorithm.

Before:
<img width="550" alt="Screenshot 2024-12-18 at 8 59 02 PM"
src="https://github.com/user-attachments/assets/75716d5f-9a40-44f4-8ffe-7a95bea7860c"
/>
After:
<img width="550" alt="Screenshot 2024-12-18 at 8 59 33 PM"
src="https://github.com/user-attachments/assets/34fa7543-a963-4de6-a185-5e274a65569c"
/>

libs/aws/langchain_aws/graphs/neptune_graph.py

@@ -3,6 +3,46 @@
 from typing import Any, Dict, List, Optional, Tuple, Union
 
 
+def _format_triples(triples: List[dict]) -> List[str]:
+    triple_template = "(:`{a}`)-[:`{e}`]->(:`{b}`)"
+    triple_schema = []
+    for t in triples:
+        triple = triple_template.format(
+            a=t["~from"], e=t["~type"], b=t["~to"]
+        )
+        triple_schema.append(triple)
+
+    return triple_schema
+
+
+def _format_node_properties(n_labels: dict) -> List:
+    node_properties = []
+
+    for label, props_item in n_labels.items():
+        props = props_item["properties"]
+        np = {
+            "properties": [{"property": k, "type": v["datatypes"][0]} for k, v in props.items()],
+            "labels": label,
+        }
+        node_properties.append(np)
+
+    return node_properties
+
+
+def _format_edge_properties(e_labels: dict) -> List:
+    edge_properties = []
+
+    for label, props_item in e_labels.items():
+        props = props_item["properties"]
+        np = {
+            "type": label,
+            "properties": [{"property": k, "type": v["datatypes"][0]} for k, v in props.items()],
+        }
+        edge_properties.append(np)
+
+    return edge_properties
+
+
 class NeptuneQueryException(Exception):
     """Exception for the Neptune queries."""
 
@@ -170,7 +210,7 @@ def __init__(
         graph_identifier: str,
         client: Any = None,
         credentials_profile_name: Optional[str] = None,
-        region_name: Optional[str] = None,
+        region_name: Optional[str] = None
     ) -> None:
         """Create a new Neptune Analytics graph wrapper instance."""
 
@@ -266,6 +306,30 @@ def _get_summary(self) -> Dict:
         else:
             return summary
 
+    def _refresh_schema(self) -> None:
+        """
+        Refreshes the Neptune graph schema information.
+        """
+        pg_schema_query = """
+        CALL neptune.graph.pg_schema() 
+        YIELD schema
+        RETURN schema
+        """
+
+        data = self.query(pg_schema_query)
+        raw_schema = data[0]["schema"]
+        triple_schema = _format_triples(raw_schema["labelTriples"])
+        node_properties = _format_node_properties(raw_schema["nodeLabelDetails"])
+        edge_properties = _format_edge_properties(raw_schema["edgeLabelDetails"])
+
+        self.schema = f"""
+        Node properties are the following:
+        {node_properties}
+        Relationship properties are the following:
+        {edge_properties}
+        The relationships are the following:
+        {triple_schema}
+        """
 
 class NeptuneGraph(BaseNeptuneGraph):
     """Neptune wrapper for graph operations.