For error on prefetch_related for tracked field

model_utils/tracker.py

@@ -103,6 +103,9 @@ class DescriptorWrapper:
         else:
             instance.__dict__[self.field_name] = value
 
+    def __getattr__(self, attr):
+        return getattr(self.descriptor, attr)
+
     @staticmethod
     def cls_for_descriptor(descriptor):
         if hasattr(descriptor, '__delete__'):

tests/models.py

@@ -324,6 +324,14 @@ class ModelTrackedFK(models.Model):
     custom_tracker_without_id = ModelTracker(fields=['fk'])
 
 
+class ModelTrackedPrefetchRelatedFK(models.Model):
+    fk = models.ForeignKey('ModelTrackedFK', on_delete=models.CASCADE)
+
+    tracker = ModelTracked()
+    custom_tracker = ModelTracker(fields=['fk_id'])
+    custom_tracker_without_id = ModelTracker(fields=['fk'])
+
+
 class ModelTrackedNotDefault(models.Model):
     name = models.CharField(max_length=20)
     number = models.IntegerField()

tests/test_fields/test_field_tracker.py

@@ -15,6 +15,7 @@ from tests.models import (
     ModelTrackedFK,
     ModelTrackedMultiple,
     ModelTrackedNotDefault,
+    ModelTrackedPrefetchRelatedFK,
     Tracked,
     TrackedAbstract,
     TrackedFileField,
@@ -538,6 +539,29 @@ class FieldTrackerForeignKeyTests(FieldTrackerTestCase):
         self.assertCurrent(fk=self.instance.fk_id)
 
 
+class ModelTrackedPrefetchRelatedFKTests(FieldTrackerTestCase):
+    """Test that using `prefetch_related` on a tracked field does raise a ValueError."""
+
+    tracked_class = ModelTrackedPrefetchRelatedFK
+
+    def setUp(self):
+        model_tracked = ModelTracked.objects.create(name="", number=0)
+        model_tracked_fk = ModelTrackedFK.objects.create(fk=model_tracked)
+        self.instance = ModelTrackedPrefetchRelatedFK.objects.create(fk=model_tracked_fk)
+
+    def test_default(self):
+        self.tracker = self.instance.tracker
+        self.assertIsNotNone(list(self.tracked_class.objects.prefetch_related("fk__fk")))
+
+    def test_custom(self):
+        self.tracker = self.instance.custom_tracker
+        self.assertIsNotNone(list(self.tracked_class.objects.prefetch_related("fk__fk")))
+
+    def test_custom_without_id(self):
+        self.tracker = self.instance.custom_tracker_without_id
+        self.assertIsNotNone(list(self.tracked_class.objects.prefetch_related("fk__fk")))
+
+
 class FieldTrackerTimeStampedTests(FieldTrackerTestCase):
 
     fk_class = Tracked