Feat: add child parent chunking method in backend. (#11598)

### What problem does this PR solve?

#7996

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

agent/component/begin.py

@@ -14,6 +14,7 @@
 #  limitations under the License.
 #
 from agent.component.fillup import UserFillUpParam, UserFillUp
+from api.db.services.file_service import FileService
 
 
 class BeginParam(UserFillUpParam):
@@ -48,7 +49,7 @@ class Begin(UserFillUp):
                 if v.get("optional") and v.get("value", None) is None:
                     v = None
                 else:
-                    v = self._canvas.get_files([v["value"]])
+                    v = FileService.get_files([v["value"]])
             else:
                 v = v.get("value")
             self.set_output(k, v)