Revert "Fix validation for ListSerializer (#8979)" (#9283)

This reverts commit e2a4559c03.

rest_framework/serializers.py

@@ -603,12 +603,6 @@ 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)
 
@@ -694,13 +688,7 @@ class ListSerializer(BaseSerializer):
         ret = []
         errors = []
 
-        for idx, item in enumerate(data):
+        for item in data:
-            if (
-                hasattr(self, 'instance')
-                and self.instance
-                and len(self.instance) > idx
-            ):
-                self.child.instance = self.instance[idx]
             try:
                 validated = self.run_child_validation(item)
             except ValidationError as exc:

tests/test_serializer.py

@@ -2,7 +2,6 @@ import inspect
 import pickle
 import re
 import sys
-import unittest
 from collections import ChainMap
 from collections.abc import Mapping
 
@@ -784,63 +783,3 @@ 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,
-            )