Fix JSON handling error for PostgreSQL graph storage

lightrag/kg/postgres_impl.py

@@ -1372,6 +1372,14 @@ class PGGraphStorage(BaseGraphStorage):
         if record:
             node = record[0]
             node_dict = node["n"]["properties"]
+            
+            # Process string result, parse it to JSON dictionary
+            if isinstance(node_dict, str):
+                try:
+                    import json
+                    node_dict = json.loads(node_dict)
+                except json.JSONDecodeError:
+                    logger.warning(f"Failed to parse node string: {node_dict}")
 
             return node_dict
         return None
@@ -1420,7 +1428,15 @@ class PGGraphStorage(BaseGraphStorage):
         record = await self._query(query)
         if record and record[0] and record[0]["edge_properties"]:
             result = record[0]["edge_properties"]
-
+            
+            # Process string result, parse it to JSON dictionary
+            if isinstance(result, str):
+                try:
+                    import json
+                    result = json.loads(result)
+                except json.JSONDecodeError:
+                    logger.warning(f"Failed to parse edge string: {result}")
+            
             return result
 
     async def get_node_edges(self, source_node_id: str) -> list[tuple[str, str]] | None:
@@ -1432,9 +1448,9 @@ class PGGraphStorage(BaseGraphStorage):
 
         query = """SELECT * FROM cypher('%s', $$
                       MATCH (n:base {entity_id: "%s"})
-                      OPTIONAL MATCH (n)-[]-(connected)
-                      RETURN n, connected
-                    $$) AS (n agtype, connected agtype)""" % (
+                      OPTIONAL MATCH (n)-[]-(connected:base)
+                      RETURN n.entity_id AS source_id, connected.entity_id AS connected_id
+                    $$) AS (source_id text, connected_id text)""" % (
             self.graph_name,
             label,
         )
@@ -1442,20 +1458,11 @@ class PGGraphStorage(BaseGraphStorage):
         results = await self._query(query)
         edges = []
         for record in results:
-            source_node = record["n"] if record["n"] else None
-            connected_node = record["connected"] if record["connected"] else None
+            source_id = record["source_id"]
+            connected_id = record["connected_id"]
 
-            if (
-                source_node
-                and connected_node
-                and "properties" in source_node
-                and "properties" in connected_node
-            ):
-                source_label = source_node["properties"].get("entity_id")
-                target_label = connected_node["properties"].get("entity_id")
-
-                if source_label and target_label:
-                    edges.append((source_label, target_label))
+            if source_id and connected_id:
+                edges.append((source_id, connected_id))
 
         return edges
 
@@ -1638,6 +1645,15 @@ class PGGraphStorage(BaseGraphStorage):
         for result in results:
             if result["node_id"] and result["n"]:
                 node_dict = result["n"]["properties"]
+                
+                # Process string result, parse it to JSON dictionary
+                if isinstance(node_dict, str):
+                    try:
+                        import json
+                        node_dict = json.loads(node_dict)
+                    except json.JSONDecodeError:
+                        logger.warning(f"Failed to parse node string in batch: {node_dict}")
+                
                 # Remove the 'base' label if present in a 'labels' property
                 if "labels" in node_dict:
                     node_dict["labels"] = [
@@ -1789,15 +1805,33 @@ class PGGraphStorage(BaseGraphStorage):
 
         for result in forward_results:
             if result["source"] and result["target"] and result["edge_properties"]:
-                edges_dict[(result["source"], result["target"])] = result[
-                    "edge_properties"
-                ]
+                edge_props = result["edge_properties"]
+                
+                # Process string result, parse it to JSON dictionary
+                if isinstance(edge_props, str):
+                    try:
+                        import json
+                        edge_props = json.loads(edge_props)
+                    except json.JSONDecodeError:
+                        logger.warning(f"Failed to parse edge properties string: {edge_props}")
+                        continue
+                
+                edges_dict[(result["source"], result["target"])] = edge_props
 
         for result in backward_results:
             if result["source"] and result["target"] and result["edge_properties"]:
-                edges_dict[(result["source"], result["target"])] = result[
-                    "edge_properties"
-                ]
+                edge_props = result["edge_properties"]
+                
+                # Process string result, parse it to JSON dictionary
+                if isinstance(edge_props, str):
+                    try:
+                        import json
+                        edge_props = json.loads(edge_props)
+                    except json.JSONDecodeError:
+                        logger.warning(f"Failed to parse edge properties string: {edge_props}")
+                        continue
+                
+                edges_dict[(result["source"], result["target"])] = edge_props
 
         return edges_dict