Minor fixes

* no need to change `raise_errors_on_nested_writes` signature
* declare nested-model outside of the test class

rest_framework/serializers.py

@@ -773,7 +773,7 @@ class ListSerializer(BaseSerializer):
 # ModelSerializer & HyperlinkedModelSerializer
 # --------------------------------------------
 
-def raise_errors_on_nested_writes(method_name, serializer, validated_data, model_field_info):
+def raise_errors_on_nested_writes(method_name, serializer, validated_data):
     """
     Give explicit errors when users attempt to pass writable nested data.
 
@@ -791,6 +791,8 @@ def raise_errors_on_nested_writes(method_name, serializer, validated_data, model
     * Silently ignore the nested part of the update.
     * Automatically create a profile instance.
     """
+    ModelClass = serializer.Meta.model
+    model_field_info = model_meta.get_field_info(ModelClass)
 
     # Ensure we don't have a writable nested field. For example:
     #
@@ -820,9 +822,7 @@ def raise_errors_on_nested_writes(method_name, serializer, validated_data, model
     #     ...
     #     address = serializer.CharField('profile.address')
     #
-    # Though, we can have a dotted field if it is not expressing a model relation.
+    # Though, non-relational fields (e.g., JSONField) are acceptable. For example:
-    #
-    # For example:
     #
     # class NonRelationalPersonModel(models.Model):
     #     profile = JSONField()
@@ -931,7 +931,7 @@ class ModelSerializer(Serializer):
         ModelClass = self.Meta.model
         info = model_meta.get_field_info(ModelClass)
 
-        raise_errors_on_nested_writes('create', self, validated_data, info)
+        raise_errors_on_nested_writes('create', self, validated_data)
 
         # Remove many-to-many relationships from validated_data.
         # They are not valid arguments to the default `.create()` method,
@@ -973,7 +973,7 @@ class ModelSerializer(Serializer):
 
     def update(self, instance, validated_data):
         info = model_meta.get_field_info(instance)
-        raise_errors_on_nested_writes('update', self, validated_data, info)
+        raise_errors_on_nested_writes('update', self, validated_data)
 
         # Simply set each attribute on the instance, and then save it.
         # Note that unlike `.create()` we don't need to treat many-to-many

tests/test_serializer_nested.py

@@ -6,7 +6,6 @@ from django.test import TestCase
 from rest_framework import serializers
 from rest_framework.compat import postgres_fields
 from rest_framework.serializers import raise_errors_on_nested_writes
-from rest_framework.utils import model_meta
 
 
 class TestNestedSerializer:
@@ -307,7 +306,13 @@ class TestNestedWriteErrors(TestCase):
         )
 
 
-@pytest.mark.skipif('not postgres_fields')
+if postgres_fields:
+    class NonRelationalPersonModel(models.Model):
+        """Model declaring a postgres JSONField"""
+        data = postgres_fields.JSONField()
+
+
+@pytest.mark.skipif(not postgres_fields, reason='psycopg2 is not installed')
 class TestNestedNonRelationalFieldWrite:
     """
     Test that raise_errors_on_nested_writes does not raise `AssertionError` when the
@@ -315,9 +320,6 @@ class TestNestedNonRelationalFieldWrite:
     """
 
     def test_nested_serializer_create_and_update(self):
-        class NonRelationalPersonModel(models.Model):
-            """Model declaring a postgres JSONField"""
-            data = postgres_fields.JSONField()
 
         class NonRelationalPersonDataSerializer(serializers.Serializer):
             occupation = serializers.CharField()
@@ -332,15 +334,10 @@ class TestNestedNonRelationalFieldWrite:
         serializer = NonRelationalPersonSerializer(data={'data': {'occupation': 'developer'}})
         assert serializer.is_valid()
         assert serializer.validated_data == {'data': {'occupation': 'developer'}}
-        ModelClass = serializer.Meta.model
+        raise_errors_on_nested_writes('create', serializer, serializer.validated_data)
-        info = model_meta.get_field_info(ModelClass)
+        raise_errors_on_nested_writes('update', serializer, serializer.validated_data)
-        raise_errors_on_nested_writes('create', serializer, serializer.validated_data, info)
-        raise_errors_on_nested_writes('update', serializer, serializer.validated_data, info)
 
     def test_dotted_source_field_create_and_update(self):
-        class NonRelationalPersonModel(models.Model):
-            """Model declaring a postgres JSONField"""
-            data = postgres_fields.JSONField()
 
         class DottedNonRelationalPersonSerializer(serializers.ModelSerializer):
             occupation = serializers.CharField(source='data.occupation')
@@ -352,8 +349,5 @@ class TestNestedNonRelationalFieldWrite:
         serializer = DottedNonRelationalPersonSerializer(data={'occupation': 'developer'})
         assert serializer.is_valid()
         assert serializer.validated_data == {'data': {'occupation': 'developer'}}
-        ModelClass = serializer.Meta.model
+        raise_errors_on_nested_writes('create', serializer, serializer.validated_data)
-        info = model_meta.get_field_info(ModelClass)
+        raise_errors_on_nested_writes('update', serializer, serializer.validated_data)
-        raise_errors_on_nested_writes('create', serializer, serializer.validated_data, info)
-        raise_errors_on_nested_writes('update', serializer, serializer.validated_data, info)
-        assert serializer.data == {'occupation': 'developer'}