Fixes instance check in ListSerializer.to_representation (#8726) (#8727)

* Fixes 'RelatedManager' object is not iterable in ListSerializer.to_representation.(#8726)

* Change to only BaseManager

* Commit unit test

* Update tests/test_serializer_lists.py

* Update tests/test_serializer_lists.py

* Update tests/test_serializer_lists.py

* Update tests/test_serializer_lists.py

* Update tests/test_serializer_lists.py

* Update tests/test_serializer_lists.py

* Format import

* Format import

Co-authored-by: Asif Saif Uddin <auvipy@gmail.com>

rest_framework/serializers.py

@@ -683,7 +683,7 @@ class ListSerializer(BaseSerializer):
         """
         # Dealing with nested relationships, data can be a Manager,
         # so, first get a queryset from the Manager if needed
-        iterable = data.all() if isinstance(data, models.Manager) else data
+        iterable = data.all() if isinstance(data, models.manager.BaseManager) else data
 
         return [
             self.child.to_representation(item) for item in iterable

tests/models.py

@@ -2,6 +2,8 @@ import uuid
 
 from django.contrib.auth.models import User
 from django.db import models
+from django.db.models import QuerySet
+from django.db.models.manager import BaseManager
 from django.utils.translation import gettext_lazy as _
 
 
@@ -124,3 +126,27 @@ class OneToOnePKSource(RESTFrameworkModel):
     target = models.OneToOneField(
         OneToOneTarget, primary_key=True,
         related_name='required_source', on_delete=models.CASCADE)
+
+
+class CustomManagerModel(RESTFrameworkModel):
+    class CustomManager:
+        def __new__(cls, *args, **kwargs):
+            cls = BaseManager.from_queryset(
+                QuerySet
+            )
+            return cls
+
+    objects = CustomManager()()
+    # `CustomManager()` will return a `BaseManager` class.
+    # We need to instantiation it, so we write `CustomManager()()` here.
+
+    text = models.CharField(
+        max_length=100,
+        verbose_name=_("Text comes here"),
+        help_text=_("Text description.")
+    )
+
+    o2o_target = models.ForeignKey(OneToOneTarget,
+                                   help_text='OneToOneTarget',
+                                   verbose_name='OneToOneTarget',
+                                   on_delete=models.CASCADE)

tests/test_serializer_lists.py

@@ -6,6 +6,9 @@ from django.utils.datastructures import MultiValueDict
 
 from rest_framework import serializers
 from rest_framework.exceptions import ErrorDetail
+from tests.models import (
+    CustomManagerModel, NullableOneToOneSource, OneToOneTarget
+)
 
 
 class BasicObject:
@@ -683,3 +686,43 @@ class TestMaxMinLengthListSerializer:
         assert min_serializer.validated_data == input_data
 
         assert not max_min_serializer.is_valid()
+
+
+@pytest.mark.django_db()
+class TestToRepresentationManagerCheck:
+    """
+    https://github.com/encode/django-rest-framework/issues/8726
+    """
+
+    def setup_method(self):
+        class CustomManagerModelSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = CustomManagerModel
+                fields = '__all__'
+
+        class OneToOneTargetSerializer(serializers.ModelSerializer):
+            my_model = CustomManagerModelSerializer(many=True, source="custommanagermodel_set")
+
+            class Meta:
+                model = OneToOneTarget
+                fields = '__all__'
+                depth = 3
+
+        class NullableOneToOneSourceSerializer(serializers.ModelSerializer):
+            target = OneToOneTargetSerializer()
+
+            class Meta:
+                model = NullableOneToOneSource
+                fields = '__all__'
+
+        self.serializer = NullableOneToOneSourceSerializer
+
+    def test(self):
+        o2o_target = OneToOneTarget.objects.create(name='OneToOneTarget')
+        NullableOneToOneSource.objects.create(
+            name='NullableOneToOneSource',
+            target=o2o_target
+        )
+        queryset = NullableOneToOneSource.objects.all()
+        serializer = self.serializer(queryset, many=True)
+        assert serializer.data