Fix backward compatibility issues in model checkpoint loading (#4199)

src/otx/core/model/base.py

@@ -389,6 +389,13 @@ def on_load_checkpoint(self, checkpoint: dict[str, Any]) -> None:
         super().on_load_checkpoint(checkpoint)
 
         if ckpt_label_info := checkpoint.get("label_info", None):
+            if isinstance(ckpt_label_info, LabelInfo) and not hasattr(ckpt_label_info, "label_ids"):
+                # NOTE: This is for backward compatibility
+                ckpt_label_info = LabelInfo(
+                    label_groups=ckpt_label_info.label_groups,
+                    label_names=ckpt_label_info.label_names,
+                    label_ids=[str(i) for i in range(len(ckpt_label_info.label_names))],
+                )
             self._label_info = ckpt_label_info
 
         if ckpt_tile_config := checkpoint.get("tile_config", None):

src/otx/engine/engine.py

@@ -594,6 +594,12 @@ def export(
                 kwargs_user_input.update(infer_reference_info_root=self.model.infer_reference_info_root)
 
             model_cls = self.model.__class__
+            if hasattr(self.model, "model_name"):
+                # NOTE: This is a solution to fix backward compatibility issue.
+                # If the model has `model_name` attribute, it will be passed to the `load_from_checkpoint` method,
+                # making sure previous model trained without model_name can be loaded.
+                kwargs_user_input["model_name"] = self.model.model_name
+
             self.model = model_cls.load_from_checkpoint(
                 checkpoint_path=checkpoint,
                 map_location="cpu",