Pass correct initial_data to ListSerializer child (#5345)

rest_framework/serializers.py

@@ -631,6 +631,7 @@ def to_internal_value(self, data):
         errors = []
 
         for item in data:
+            self.child.initial_data = item
             try:
                 validated = self.child.run_validation(item)
             except ValidationError as exc:
@@ -669,9 +670,20 @@ def update(self, instance, validated_data):
         )
 
     def create(self, validated_data):
-        return [
-            self.child.create(attrs) for attrs in validated_data
-        ]
+        ret = []
+        if hasattr(self, 'initial_data'):
+            initial_data = self.initial_data
+            if html.is_html_input(initial_data):
+                initial_data = html.parse_html_list(initial_data)
+        else:
+            initial_data = None
+
+        for i, attrs in enumerate(validated_data):
+            if initial_data is not None:
+                self.child.initial_data = initial_data[i]
+            ret.append(self.child.create(attrs))
+
+        return ret
 
     def save(self, **kwargs):
         """

tests/test_serializer_lists.py

@@ -138,6 +138,70 @@ def test_validate_html_input(self):
         assert serializer.is_valid()
         assert serializer.validated_data == expected_output
 
+    def test_validate_initial_data(self):
+        data = [{"field": "value1"}, {"field": "value2"}]
+        expected_initial_data = list(data)
+
+        class AssertingChildSerializer(serializers.Serializer):
+            def validate(self, attrs):
+                assert self.initial_data == expected_initial_data.pop(0)
+                return attrs
+
+        serializer = AssertingChildSerializer(data=list(data), many=True)
+        assert serializer.is_valid()
+        assert len(expected_initial_data) == 0
+
+    def test_create_initial_data(self):
+        data = [{"field": "value1"}, {"field": "value2"}]
+        expected_initial_data = list(data)
+
+        class AssertingChildSerializer(serializers.Serializer):
+            field = serializers.CharField()
+
+            def create(self, validated_data):
+                assert self.initial_data == expected_initial_data.pop(0)
+                return validated_data
+
+        serializer = AssertingChildSerializer(data=data, many=True)
+        assert serializer.is_valid()
+        assert serializer.save() == data
+        assert len(expected_initial_data) == 0
+
+    def test_validate_initial_data_html_input(self):
+        expected_initial_data = [{"field": ["value1"]}, {"field": ["value2"]}]
+
+        class AssertingChildSerializer(serializers.Serializer):
+            def validate(self, attrs):
+                assert self.initial_data == expected_initial_data.pop(0)
+                return attrs
+
+        initial_data = MultiValueDict({
+            "[0]field": ["value1"],
+            "[1]field": ["value2"],
+        })
+        serializer = AssertingChildSerializer(data=initial_data, many=True)
+        assert serializer.is_valid()
+        assert len(expected_initial_data) == 0
+
+    def test_create_initial_data_html_input(self):
+        expected_initial_data = [{"field": ["value1"]}, {"field": ["value2"]}]
+
+        class AssertingChildSerializer(serializers.Serializer):
+            field = serializers.CharField()
+
+            def create(self, validated_data):
+                assert self.initial_data == expected_initial_data.pop(0)
+                return validated_data
+
+        initial_data = MultiValueDict({
+            "[0]field": ["value1"],
+            "[1]field": ["value2"],
+        })
+        serializer = AssertingChildSerializer(data=initial_data, many=True)
+        assert serializer.is_valid()
+        assert serializer.save() == [{"field": "value1"}, {"field": "value2"}]
+        assert len(expected_initial_data) == 0
+
 
 class TestNestedListSerializer:
     """