fix(api): adding variable to variable pool recursively while loading draft variables. (#21478)

This PR fix the issue that `ObjectSegment` are not recursively added to the draft variable pool while loading draft variables from database. It also fixes an issue about loading variables with more than two elements in the its selector.

Enhances #19735.
Closes #21477.

api/core/workflow/graph_engine/graph_engine.py

@@ -53,6 +53,7 @@ from core.workflow.nodes.end.end_stream_processor import EndStreamProcessor
 from core.workflow.nodes.enums import ErrorStrategy, FailBranchSourceHandle
 from core.workflow.nodes.event import RunCompletedEvent, RunRetrieverResourceEvent, RunStreamChunkEvent
 from core.workflow.nodes.node_mapping import NODE_TYPE_CLASSES_MAPPING
+from core.workflow.utils import variable_utils
 from libs.flask_utils import preserve_flask_contexts
 from models.enums import UserFrom
 from models.workflow import WorkflowType
@@ -856,16 +857,12 @@ class GraphEngine:
         :param variable_value: variable value
         :return:
         """
-        self.graph_runtime_state.variable_pool.add([node_id] + variable_key_list, variable_value)
-
-        # if variable_value is a dict, then recursively append variables
-        if isinstance(variable_value, dict):
-            for key, value in variable_value.items():
-                # construct new key list
-                new_key_list = variable_key_list + [key]
-                self._append_variables_recursively(
-                    node_id=node_id, variable_key_list=new_key_list, variable_value=value
-                )
+        variable_utils.append_variables_recursively(
+            self.graph_runtime_state.variable_pool,
+            node_id,
+            variable_key_list,
+            variable_value,
+        )
 
     def _is_timed_out(self, start_at: float, max_execution_time: int) -> bool:
         """