Fix validation for ListSerializer (#8979)

* fix: Make the instance variable of child serializer point to the correct list object instead of the entire list when validating ListSerializer

* fix formatting issues for list serializer validation fix

* fix imports sorting for list serializer tests

* remove django 2.2 from docs index (#8982)

* Declared Django 4.2 support in README.md (#8985)

* Fix Links in Documentation to Django `reverse` and `reverse_lazy` (#8986)

* Fix Django Docs url in reverse.md

Django URLs of the documentation of `reverse` and `reverse_lazy` were wrong.

* Update reverse.md

* fix URLPathVersioning reverse fallback (#7247)

* fix URLPathVersioning reverse fallback

* add test for URLPathVersioning reverse fallback

* Update tests/test_versioning.py

---------

Co-authored-by: Jorn van Wier <jorn.van.wier@thunderbyte.ai>
Co-authored-by: Asif Saif Uddin <auvipy@gmail.com>

* Make set_value a method within `Serializer` (#8001)

* Make set_value a static method for Serializers

As an alternative to #7671, let the method be overridden if needed. As
the function is only used for serializers, it has a better place in the
Serializer class.

* Set `set_value` as an object (non-static) method

* Add tests for set_value()

These tests follow the examples given in the method.

* fix: Make the instance variable of child serializer point to the correct list object instead of the entire list when validating ListSerializer

* Make set_value a method within `Serializer` (#8001)

* Make set_value a static method for Serializers

As an alternative to #7671, let the method be overridden if needed. As
the function is only used for serializers, it has a better place in the
Serializer class.

* Set `set_value` as an object (non-static) method

* Add tests for set_value()

These tests follow the examples given in the method.

* fix: Make the instance variable of child serializer point to the correct list object instead of the entire list when validating ListSerializer

* fix: Make the instance variable of child serializer point to the correct list object instead of the entire list when validating ListSerializer

* fix formatting issues for list serializer validation fix

* fix: Make the instance variable of child serializer point to the correct list object instead of the entire list when validating ListSerializer

* fix formatting issues for list serializer validation fix

* fix linting

* Update rest_framework/serializers.py

Co-authored-by: Sergei Shishov <sshishov@users.noreply.github.com>

* Update rest_framework/serializers.py

Co-authored-by: Sergei Shishov <sshishov@users.noreply.github.com>

* fix: instance variable in list serializer, remove commented code

---------

Co-authored-by: Mathieu Dupuy <deronnax@gmail.com>
Co-authored-by: Mehraz Hossain Rumman <59512321+MehrazRumman@users.noreply.github.com>
Co-authored-by: Dominik Bruhn <dominik@dbruhn.de>
Co-authored-by: jornvanwier <mail@jornvanwier.com>
Co-authored-by: Jorn van Wier <jorn.van.wier@thunderbyte.ai>
Co-authored-by: Asif Saif Uddin <auvipy@gmail.com>
Co-authored-by: Étienne Beaulé <beauleetienne0@gmail.com>
Co-authored-by: Sergei Shishov <sshishov@users.noreply.github.com>

rest_framework/serializers.py

@@ -609,6 +609,12 @@ class ListSerializer(BaseSerializer):
         self.min_length = kwargs.pop('min_length', None)
         assert self.child is not None, '`child` is a required argument.'
         assert not inspect.isclass(self.child), '`child` has not been instantiated.'
+
+        instance = kwargs.get('instance', [])
+        data = kwargs.get('data', [])
+        if instance and data:
+            assert len(data) == len(instance), 'Data and instance should have same length'
+
         super().__init__(*args, **kwargs)
         self.child.bind(field_name='', parent=self)
 
@@ -683,7 +689,13 @@ class ListSerializer(BaseSerializer):
         ret = []
         errors = []
 
-        for item in data:
+        for idx, item in enumerate(data):
+            if (
+                hasattr(self, 'instance')
+                and self.instance
+                and len(self.instance) > idx
+            ):
+                self.child.instance = self.instance[idx]
             try:
                 validated = self.child.run_validation(item)
             except ValidationError as exc:

tests/test_serializer.py

@@ -2,6 +2,7 @@ import inspect
 import pickle
 import re
 import sys
+import unittest
 from collections import ChainMap
 from collections.abc import Mapping
 
@@ -783,3 +784,63 @@ class TestSetValueMethod:
         ret = {'a': 1}
         self.s.set_value(ret, ['x', 'y'], 2)
         assert ret == {'a': 1, 'x': {'y': 2}}
+
+
+class MyClass(models.Model):
+    name = models.CharField(max_length=100)
+    value = models.CharField(max_length=100, blank=True)
+
+    app_label = "test"
+
+    @property
+    def is_valid(self):
+        return self.name == 'valid'
+
+
+class MyClassSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = MyClass
+        fields = ('id', 'name', 'value')
+
+    def validate_value(self, value):
+        if value and not self.instance.is_valid:
+            raise serializers.ValidationError(
+                'Status cannot be set for invalid instance')
+        return value
+
+
+class TestMultipleObjectsValidation(unittest.TestCase):
+    def setUp(self):
+        self.objs = [
+            MyClass(name='valid'),
+            MyClass(name='invalid'),
+            MyClass(name='other'),
+        ]
+
+    def test_multiple_objects_are_validated_separately(self):
+
+        serializer = MyClassSerializer(
+            data=[{'value': 'set', 'id': instance.id} for instance in
+                  self.objs],
+            instance=self.objs,
+            many=True,
+            partial=True,
+        )
+
+        assert not serializer.is_valid()
+        assert serializer.errors == [
+            {},
+            {'value': ['Status cannot be set for invalid instance']},
+            {'value': ['Status cannot be set for invalid instance']}
+        ]
+
+    def test_exception_raised_when_data_and_instance_length_different(self):
+
+        with self.assertRaises(AssertionError):
+            MyClassSerializer(
+                data=[{'value': 'set', 'id': instance.id} for instance in
+                      self.objs],
+                instance=self.objs[:-1],
+                many=True,
+                partial=True,
+            )