properly set background on file load

src/easyreflectometry/data/data_store.py

@@ -79,9 +79,10 @@ def __init__(
         model: Optional['Model'] = None,  # delay type checking until runtime (quotes)
         x_label: str = 'x',
         y_label: str = 'y',
+        auto_background: bool = True,
     ):
         self._model = model
-        if y is not None and model is not None:
+        if y is not None and model is not None and auto_background:
             self._model.background = max(np.min(y), 1e-10)
 
         if x is None:
@@ -123,7 +124,6 @@ def model(self) -> 'Model':  # delay type checking until runtime (quotes)
     @model.setter
     def model(self, new_model: 'Model') -> None:
         self._model = new_model
-        self._model.background = max(np.min(self.y), 1e-10)
 
     @property
     def is_experiment(self) -> bool:

src/easyreflectometry/project.py

@@ -402,6 +402,12 @@
         """
         model.resolution_function = PercentageFwhm(5.0)
 
+    @staticmethod
+    def _auto_set_background(experiment: DataSet1D) -> None:
+        """Set the model background to the minimum y-value of the experiment data."""
+        if experiment.model is not None and len(experiment.y) > 0:
+            experiment.model.background = max(np.min(experiment.y), 1e-10)
+
     def load_new_experiment(self, path: Union[Path, str]) -> None:
         new_experiment = load_as_dataset(str(path))
         new_index = len(self._experiments)
@@ -412,6 +418,7 @@
 
         self._apply_experiment_metadata(path, new_experiment, f'Experiment {new_index}')
         new_experiment.model = self.models[model_index]
+        self._auto_set_background(new_experiment)
         self._experiments[new_index] = new_experiment
         self._with_experiments = True
         self._apply_resolution_function(new_experiment, self.models[model_index])
@@ -473,6 +480,7 @@
                 data_key=data_key,
             )
             new_experiment.model = self.models[model_index]
+            self._auto_set_background(new_experiment)
             self._experiments[new_index] = new_experiment
             self._apply_resolution_function(new_experiment, self.models[model_index])
 
@@ -484,6 +492,7 @@
 
         self._apply_experiment_metadata(path, experiment, f'Experiment {index}')
         experiment.model = self.models[index]
+        self._auto_set_background(experiment)
         self._experiments[index] = experiment
         self._with_experiments = True
         self._apply_resolution_function(experiment, self._models[index])
@@ -727,6 +736,7 @@
                 ye=project_dict['experiments'][key][2],
                 xe=project_dict['experiments'][key][3],
                 model=self._models[project_dict['experiments_models'][key]],
+                auto_background=False,
             )
         return experiments
 

tests/data/test_data_store.py

@@ -79,16 +79,17 @@ def test_model_property(self):
         # Then
         assert data.model == mock_model
 
-    def test_model_setter_updates_background(self):
+    def test_model_setter_does_not_update_background(self):
         # Given
         mock_model = Mock()
+        mock_model.background = 1e-8  # Original background value
         data = DataSet1D(x=[1, 2, 3, 4], y=[1, 2, 0.5, 3])
 
         # When
         data.model = mock_model
 
-        # Then
-        assert mock_model.background == 0.5
+        # Then - background should NOT be overwritten by model setter
+        assert mock_model.background == 1e-8
 
     def test_is_experiment_property(self):
         # Given

tests/test_measurement_comprehensive.py

@@ -189,14 +189,15 @@ def test_data_points_iterator(self):
         expected = [(1, 10, 1, 0.1), (2, 20, 2, 0.2), (3, 30, 3, 0.3)]
         assert points == expected
 
-    def test_model_property_with_background_setting(self):
-        """Test that setting model updates background to minimum y value."""
+    def test_model_property_setter_does_not_update_background(self):
+        """Test that setting model via setter does not overwrite background."""
         dataset = DataSet1D(x=[1, 2, 3, 4], y=[5, 1, 8, 3])
         mock_model = Mock()
+        mock_model.background = 1e-8  # Original value
 
         dataset.model = mock_model
 
-        assert mock_model.background == 1  # minimum of [5, 1, 8, 3]
+        assert mock_model.background == 1e-8  # background should NOT be changed by setter
 
     def test_repr_string_representation(self):
         """Test the string representation of DataSet1D."""