Update docs and tests for custom field validation

Author: Johan van den Dorpe

changes/205.fixed

@@ -0,0 +1 @@
+Added support for validating custom fields by referencing them as cf_<custom_field_name> in ComplianceError exceptions

docs/user/app_data_compliance.md

@@ -18,6 +18,9 @@ Any `DataComplianceRule` class can have a `name` defined to provide a friendly n
 > 
 > For example, if a user fixes an object attribute that was incompliant with a built-in rule and then navigates to its `Data Compliance` tab, the object will still show as invalid for that built-in rule. This will remain the case until the job is ran again with the `Run built-in validation rules?` option checked.
 
+!!! note
+    When raising a ComplianceError, the attribute must exist on the object. To raise errors for custom fields, use cf_custom_field_name as the attribute name.
+
 ## How to Use
 
 ### Step 1. Create Data Compliance Rules

nautobot_data_validation_engine/tests/test_data_compliance_rules.py

@@ -78,3 +78,34 @@ def test_validate_replaces_results(self):
             len(DataCompliance.objects.filter(compliance_class_name=TestFailedDataComplianceRule.__name__)),
             5,
         )
+
+    def test_custom_field_attribute_value(self):
+        # Simulate a Location with a custom field value
+        self.s.cf = {"foo": "bar"}
+        # Patch DataComplianceRule.context to include our instance
+        rule = TestPassedDataComplianceRule(self.s)
+        rule.context = {"object": self.s}
+
+        # Call _create_data_compliance_object with a custom field attribute
+        obj = rule._create_data_compliance_object(attribute="cf_foo", valid=True, message="msg")
+        self.assertEqual(obj.validated_attribute, "cf_foo")
+        self.assertEqual(obj.validated_attribute_value, "bar")
+
+    def test_custom_field_attribute_value_missing(self):
+        # Simulate a Location with no custom field value
+        self.s.cf = {}
+        rule = TestPassedDataComplianceRule(self.s)
+        rule.context = {"object": self.s}
+
+        obj = rule._create_data_compliance_object(attribute="cf_missing", valid=True, message="msg")
+        self.assertEqual(obj.validated_attribute, "cf_missing")
+        self.assertIsNone(obj.validated_attribute_value)
+
+    def test_regular_attribute_value(self):
+        # Test with a regular attribute
+        rule = TestPassedDataComplianceRule(self.s)
+        rule.context = {"object": self.s}
+
+        obj = rule._create_data_compliance_object(attribute="name", valid=True, message="msg")
+        self.assertEqual(obj.validated_attribute, "name")
+        self.assertEqual(obj.validated_attribute_value, self.s.name)