Validate properties in __set__.

This uses the existing validation logic in `PropertyInfo` to check assignments made in Python as well as set operations over HTTP.

Author: rwb27

src/labthings_fastapi/properties.py

@@ -608,7 +608,8 @@ def __set__(
         :param value: the new value for the property.
         :param emit_changed_event: whether to emit a changed event.
         """
-        obj.__dict__[self.name] = value
+        property_info = self.descriptor_info(obj)
+        obj.__dict__[self.name] = property_info.validate(value)
         if emit_changed_event:
             self.emit_changed_event(obj, value)
 
@@ -811,13 +812,19 @@ def instance_get(self, obj: Owner) -> Value:
     def __set__(self, obj: Owner, value: Value) -> None:
         """Set the value of the property.
 
+        This will validate the value against the property's model, and an error
+        will be raised if the value is not valid.
+
         :param obj: the `.Thing` on which the attribute is accessed.
         :param value: the value of the property.
 
         :raises ReadOnlyPropertyError: if the property cannot be set.
         """
         if self.fset is None:
             raise ReadOnlyPropertyError(f"Property {self.name} of {obj} has no setter.")
+        property_info = self.descriptor_info(obj)
+        value = property_info.validate(value)
+
         self.fset(obj, value)
 
 

tests/test_properties.py

@@ -378,21 +378,44 @@ def test_setting_without_event_loop():
 
 
 @pytest.mark.parametrize("prop_info", CONSTRAINED_PROPS)
-def test_constrained_properties(prop_info):
-    """Test that constraints on property values generate correct models."""
+def test_constrained_properties(prop_info, mocker):
+    """Test that constraints on property values generate correct models.
+
+    This also tests the `validate` method and checks validation happens
+    on assignment to the property in Python. Further checks over http
+    are made in later tests.
+    """
     prop = prop_info.prop
     assert prop.value_type is prop_info.value_type
     m = prop.model
     assert issubclass(m, RootModel)
+    mock_thing = mocker.Mock(spec=PropertyTestThing)
+    mock_thing._thing_server_interface = mocker.Mock()
+    descriptorinfo = prop.descriptor_info(mock_thing)
+    assert isinstance(descriptorinfo, PropertyInfo)
     for ann in prop_info.constraints:
         assert any(meta == ann for meta in m.model_fields["root"].metadata)
     for valid in prop_info.valid_values:
+        # Check the model can be created
         instance = m(root=valid)
+        # Check the value passes through the model
         validated = instance.model_dump()
         assert validated == valid or validated is valid  # `is` for NaN
+        # Check the descriptorinfo object also validates
+        # (this is what we get from thing.properties["name"])
+        validated = descriptorinfo.validate(valid)
+        assert validated == valid or validated is valid  # `is` for NaN
+        # Check that assignment works
+        prop.__set__(mock_thing, valid)
+        validated = prop.__get__(mock_thing)
+        assert validated == valid or validated is valid  # `is` for NaN
     for invalid in prop_info.invalid_values:
         with pytest.raises(ValidationError):
             _ = m(root=invalid)
+        with pytest.raises(ValidationError):
+            descriptorinfo.validate(invalid)
+        with pytest.raises(ValidationError):
+            prop.__set__(mock_thing, invalid)
 
 
 def convert_inf_nan(value):

tests/test_property.py

@@ -365,8 +365,8 @@ class BadIntModel(pydantic.BaseModel):
     # Check that a broken `_model` raises the right error
     # See above for where we manually set badprop._model to something that's
     # not a rootmodel.
-    example.badprop = 3
-    assert example.badprop == 3
+    with pytest.raises(TypeError):
+        example.badprop = 3  # Validation will fail here because of the bad model.
     with pytest.raises(TypeError):
         _ = example.properties["badprop"].model_instance
     with pytest.raises(TypeError):