Fixed #31044 -- Errored nicely when using Prefetch with a raw() queryset.

1 files changed, 9 insertions, 2 deletions

diff --git a/django/db/models/query.py b/django/db/models/query.py
index 73991df7bb..764d3ea289 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -1534,8 +1534,15 @@ class Prefetch:
         self.prefetch_through = lookup
         # `prefetch_to` is the path to the attribute that stores the result.
         self.prefetch_to = lookup
-        if queryset is not None and not issubclass(queryset._iterable_class, ModelIterable):
-            raise ValueError('Prefetch querysets cannot use values().')
+        if queryset is not None and (
+            isinstance(queryset, RawQuerySet) or (
+                hasattr(queryset, '_iterable_class') and
+                not issubclass(queryset._iterable_class, ModelIterable)
+            )
+        ):
+            raise ValueError(
+                'Prefetch querysets cannot use raw() and values().'
+            )
         if to_attr:
             self.prefetch_to = LOOKUP_SEP.join(lookup.split(LOOKUP_SEP)[:-1] + [to_attr])