fixed bug when replacing of existing sample in GUI

src/easyreflectometry/project.py

@@ -438,8 +438,17 @@
 
     @models.setter
     def models(self, models: ModelCollection) -> None:
-        """Models function."""
+        """Models function.
+
+        A loaded experiment whose model is dropped is bound to the new model at
+        the same index, or to the first one when there are fewer.
+        """
+        old_indices = {key: self._model_index(experiment.model) for key, experiment in self._experiments.items()}
         self._replace_collection(models, self._models)
+        for key, experiment in self._experiments.items():
+            if old_indices[key] is not None and self._model_index(experiment.model) is None and len(self._models):
+                index = old_indices[key] if old_indices[key] < len(self._models) else 0
+                experiment.model = self._models[index]
         self._invalidate_fitter()
         # Use setter to update indicies for current model, assembly and layer
         self.current_model_index = 0

tests/test_project.py

@@ -1288,6 +1288,19 @@ def test_replace_models_from_orso(self):
         # Current model index should be reset to 0
         assert project.current_model_index == 0
 
+    def test_replace_models_from_orso_rebinds_loaded_experiments(self):
+        """An experiment loaded before the models are replaced follows the new model and can be fitted."""
+        global_object.map._clear()
+        project = Project()
+        project.default_model()
+        project.load_new_experiment(os.path.join(PATH_STATIC, 'Ni_example.ort'))
+
+        sample = Sample(Multilayer([Layer(material=Material(sld=5.0, isld=0.0), thickness=50, roughness=2)]))
+        project.replace_models_from_orso(sample)
+
+        assert project.experiments[0].model is project.models[0]
+        assert project.prepare_fit().skipped == []
+
     def test_is_default_model_true(self):
         # When
         global_object.map._clear()