fix(api): serialize pipeline file-upload created_at (#32098)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/controllers/service_api/dataset/rag_pipeline/rag_pipeline_workflow.py

@@ -10,6 +10,7 @@ from controllers.common.errors import FilenameNotExistsError, NoFileUploadedErro
 from controllers.common.schema import register_schema_model
 from controllers.service_api import service_api_ns
 from controllers.service_api.dataset.error import PipelineRunError
+from controllers.service_api.dataset.rag_pipeline.serializers import serialize_upload_file
 from controllers.service_api.wraps import DatasetApiResource
 from core.app.apps.pipeline.pipeline_generator import PipelineGenerator
 from core.app.entities.app_invoke_entities import InvokeFrom
@@ -230,12 +231,4 @@ class KnowledgebasePipelineFileUploadApi(DatasetApiResource):
         except services.errors.file.UnsupportedFileTypeError:
             raise UnsupportedFileTypeError()
 
-        return {
-            "id": upload_file.id,
-            "name": upload_file.name,
-            "size": upload_file.size,
-            "extension": upload_file.extension,
-            "mime_type": upload_file.mime_type,
-            "created_by": upload_file.created_by,
-            "created_at": upload_file.created_at,
-        }, 201
+        return serialize_upload_file(upload_file), 201

api/controllers/service_api/dataset/rag_pipeline/serializers.py

@@ -0,0 +1,22 @@
+"""
+Serialization helpers for Service API knowledge pipeline endpoints.
+"""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Any
+
+if TYPE_CHECKING:
+    from models.model import UploadFile
+
+
+def serialize_upload_file(upload_file: UploadFile) -> dict[str, Any]:
+    return {
+        "id": upload_file.id,
+        "name": upload_file.name,
+        "size": upload_file.size,
+        "extension": upload_file.extension,
+        "mime_type": upload_file.mime_type,
+        "created_by": upload_file.created_by,
+        "created_at": upload_file.created_at.isoformat() if upload_file.created_at else None,
+    }