fix(workflow): fix node link to previous node issue

api/core/workflow/graph_engine/entities/graph.py

@@ -1,6 +1,7 @@
 import uuid
 from collections.abc import Mapping
 from typing import Any, Optional, cast
+from cycler import V
 
 from pydantic import BaseModel, Field
 
@@ -152,6 +153,12 @@ class Graph(BaseModel):
 
         if not root_node_id or root_node_id not in root_node_ids:
             raise ValueError(f"Root node id {root_node_id} not found in the graph")
+        
+        # Check whether it is connected to the previous node
+        cls._check_connected_to_previous_node(
+            route=[root_node_id],
+            edge_mapping=edge_mapping
+        )
 
         # fetch all node ids from root node
         node_ids = [root_node_id]
@@ -267,6 +274,30 @@ class Graph(BaseModel):
                 node_id=graph_edge.target_node_id
             )
 
+    @classmethod
+    def _check_connected_to_previous_node(
+        cls, 
+        route: list[str],
+        edge_mapping: dict[str, list[GraphEdge]]
+    ) -> None:
+        """
+        Check whether it is connected to the previous node
+        """
+        new_route = list(route)
+
+        for graph_edge in edge_mapping.get(new_route[-1], []):
+            if not graph_edge.target_node_id:
+                continue
+
+            if graph_edge.target_node_id in new_route:
+                raise ValueError(f"Node {graph_edge.source_node_id} is connected to the previous node, please check the graph.")
+
+            new_route.append(graph_edge.target_node_id)
+            cls._check_connected_to_previous_node(
+                route=new_route,
+                edge_mapping=edge_mapping,
+            )
+
     @classmethod
     def _recursively_add_parallels(cls,
                                    edge_mapping: dict[str, list[GraphEdge]],