From fdde44d9d1de7299a06fe618a98a5068a806e491 Mon Sep 17 00:00:00 2001
From: Laurent De Marez <laurent@demarez.org>
Date: Thu, 23 Jun 2016 17:03:24 +0200
Subject: [PATCH] Fix parsing multipart data using a nested serializer with
 list (#3820)

It is possible that a key in a MultiValueDict has multiple values, lists
are represented this way. When accessing a key in a MultiValueDict
it only returns the last element of that key. This becomes a problem
when parsing an html dict with a list inside of it.

To fix this problem we have to get and set the value using .getlist()
and .setlist().
---
 rest_framework/utils/html.py    |  6 ++++--
 tests/test_serializer_nested.py | 29 +++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/rest_framework/utils/html.py b/rest_framework/utils/html.py
index 3b871027c7..121c825c73 100644
--- a/rest_framework/utils/html.py
+++ b/rest_framework/utils/html.py
@@ -80,10 +80,12 @@ def parse_html_dict(dictionary, prefix=''):
     """
     ret = MultiValueDict()
     regex = re.compile(r'^%s\.(.+)$' % re.escape(prefix))
-    for field, value in dictionary.items():
+    for field in dictionary:
         match = regex.match(field)
         if not match:
             continue
         key = match.groups()[0]
-        ret[key] = value
+        value = dictionary.getlist(field)
+        ret.setlist(key, value)
+
     return ret
diff --git a/tests/test_serializer_nested.py b/tests/test_serializer_nested.py
index aeb092ee05..1336003995 100644
--- a/tests/test_serializer_nested.py
+++ b/tests/test_serializer_nested.py
@@ -167,3 +167,32 @@ def test_empty_not_allowed_if_allow_empty_is_set_to_false(self):
 
         expected_errors = {'not_allow_empty': {'non_field_errors': [serializers.ListSerializer.default_error_messages['empty']]}}
         assert serializer.errors == expected_errors
+
+
+class TestNestedSerializerWithList:
+    def setup(self):
+        class NestedSerializer(serializers.Serializer):
+            example = serializers.MultipleChoiceField(choices=[1, 2, 3])
+
+        class TestSerializer(serializers.Serializer):
+            nested = NestedSerializer()
+
+        self.Serializer = TestSerializer
+
+    def test_nested_serializer_with_list_json(self):
+        input_data = {
+            'nested': {
+                'example': [1, 2],
+            }
+        }
+        serializer = self.Serializer(data=input_data)
+
+        assert serializer.is_valid()
+        assert serializer.validated_data['nested']['example'] == set([1, 2])
+
+    def test_nested_serializer_with_list_multipart(self):
+        input_data = QueryDict('nested.example=1&nested.example=2')
+        serializer = self.Serializer(data=input_data)
+
+        assert serializer.is_valid()
+        assert serializer.validated_data['nested']['example'] == set([1, 2])