Fixed #2761 - ListField truncation on HTTP PATCH

rest_framework/fields.py

@@ -1262,14 +1262,13 @@ def __init__(self, *args, **kwargs):
         super(MultipleChoiceField, self).__init__(*args, **kwargs)
 
     def get_value(self, dictionary):
+        if self.field_name not in dictionary:
+            if getattr(self.root, 'partial', False):
+                return empty
         # We override the default field access in order to support
         # lists in HTML forms.
         if html.is_html_input(dictionary):
-            ret = dictionary.getlist(self.field_name)
-            if getattr(self.root, 'partial', False) and not ret:
-                ret = empty
-            return ret
-
+            return dictionary.getlist(self.field_name)
         return dictionary.get(self.field_name, empty)
 
     def to_internal_value(self, data):
@@ -1416,6 +1415,9 @@ def __init__(self, *args, **kwargs):
         self.child.bind(field_name='', parent=self)
 
     def get_value(self, dictionary):
+        if self.field_name not in dictionary:
+            if getattr(self.root, 'partial', False):
+                return empty
         # We override the default field access in order to support
         # lists in HTML forms.
         if html.is_html_input(dictionary):

tests/test_serializer_lists.py

@@ -289,3 +289,32 @@ class Meta:
         serializer = TestSerializer(data=[], many=True)
         assert not serializer.is_valid()
         assert serializer.errors == {'non_field_errors': ['Non field error']}
+
+
+class TestSerializerPartialUsage:
+    """
+    When not submitting key for list fields or multiple choice, partial
+    serialization should result in an empty state (key not there), not
+    an empty list.
+
+    Regression test for Github issue #2761.
+    """
+    def test_partial_listfield(self):
+        class ListSerializer(serializers.Serializer):
+            listdata = serializers.ListField()
+        serializer = ListSerializer(data=MultiValueDict(), partial=True)
+        result = serializer.to_internal_value(data={})
+        assert "listdata" not in result
+        assert serializer.is_valid()
+        assert serializer.validated_data == {}
+        assert serializer.errors == {}
+
+    def test_partial_multiplechoice(self):
+        class MultipleChoiceSerializer(serializers.Serializer):
+            multiplechoice = serializers.MultipleChoiceField(choices=[1, 2, 3])
+        serializer = MultipleChoiceSerializer(data=MultiValueDict(), partial=True)
+        result = serializer.to_internal_value(data={})
+        assert "multiplechoice" not in result
+        assert serializer.is_valid()
+        assert serializer.validated_data == {}
+        assert serializer.errors == {}