raise error when calling .data in an invalid serializer

rest_framework/renderers.py

@@ -34,6 +34,7 @@ from rest_framework.settings import api_settings
 from rest_framework.utils import encoders, json
 from rest_framework.utils.breadcrumbs import get_breadcrumbs
 from rest_framework.utils.field_mapping import ClassLookupDict
+from rest_framework.utils.serializer_helpers import ReturnDict
 
 
 def zero_as_none(value):
@@ -522,12 +523,14 @@ class BrowsableAPIRenderer(BaseRenderer):
             return self.render_form_for_serializer(serializer)
 
     def render_form_for_serializer(self, serializer):
-        if hasattr(serializer, 'initial_data'):
-            serializer.is_valid()
+        if hasattr(serializer, 'initial_data') and not serializer.is_valid():
+            data = ReturnDict(serializer.get_initial(), serializer=serializer)
+        else:
+            data = serializer.data
 
         form_renderer = self.form_renderer_class()
         return form_renderer.render(
-            serializer.data,
+            data,
             self.accepted_media_type,
             {'style': {'template_pack': 'rest_framework/horizontal'}}
         )

rest_framework/serializers.py

@@ -262,6 +262,9 @@ class BaseSerializer(Field):
                 self._data = self.to_representation(self.instance)
             elif hasattr(self, '_validated_data') and not getattr(self, '_errors', None):
                 self._data = self.to_representation(self.validated_data)
+            elif hasattr(self, '_validated_data') and getattr(self, '_errors', None):
+                msg = 'You can not access `.data` in an invalid serializer.'
+                raise AssertionError(msg)
             else:
                 self._data = self.get_initial()
         return self._data
@@ -547,7 +550,13 @@ class Serializer(BaseSerializer):
 
     def __getitem__(self, key):
         field = self.fields[key]
-        value = self.data.get(key)
+
+        # If the data is not valid, return the initial data
+        if not hasattr(self, '_data') and hasattr(self, '_validated_data') and getattr(self, '_errors', None):
+            value = self.get_initial().get(key)
+        else:
+            value = self.data.get(key)
+
         error = self.errors.get(key) if hasattr(self, '_errors') else None
         if isinstance(field, Serializer):
             return NestedBoundField(field, value, error)

rest_framework/templatetags/rest_framework.py

@@ -13,6 +13,7 @@ from django.utils.safestring import SafeData, mark_safe
 
 from rest_framework.compat import apply_markdown, pygments_highlight
 from rest_framework.renderers import HTMLFormRenderer
+from rest_framework.utils.serializer_helpers import ReturnDict
 from rest_framework.utils.urls import replace_query_param
 
 register = template.Library()
@@ -79,9 +80,14 @@ def get_pagination_html(pager):
 
 @register.simple_tag
 def render_form(serializer, template_pack=None):
+    if hasattr(serializer, 'initial_data') and not serializer.is_valid():
+        data = ReturnDict(serializer.get_initial(), serializer=serializer)
+    else:
+        data = serializer.data
+
     style = {'template_pack': template_pack} if template_pack else {}
     renderer = HTMLFormRenderer()
-    return renderer.render(serializer.data, None, {'style': style})
+    return renderer.render(data, None, {'style': style})
 
 
 @register.simple_tag

tests/test_renderers.py

@@ -499,7 +499,7 @@ class TestHTMLFormRenderer(TestCase):
             test_field = serializers.CharField()
 
         self.renderer = HTMLFormRenderer()
-        self.serializer = TestSerializer(data={})
+        self.serializer = TestSerializer(data={'test_field': 'test'})
 
     def test_render_with_default_args(self):
         self.serializer.is_valid()

tests/test_serializer.py

@@ -86,15 +86,17 @@ class TestSerializer:
         serializer = self.Serializer(data={'char': 'abc'})
         assert not serializer.is_valid()
         assert serializer.validated_data == {}
-        assert serializer.data == {'char': 'abc'}
         assert serializer.errors == {'integer': ['This field is required.']}
+        with pytest.raises(AssertionError):
+            serializer.data
 
     def test_invalid_datatype(self):
         serializer = self.Serializer(data=[{'char': 'abc'}])
         assert not serializer.is_valid()
         assert serializer.validated_data == {}
-        assert serializer.data == {}
         assert serializer.errors == {'non_field_errors': ['Invalid data. Expected a dictionary, but got list.']}
+        with pytest.raises(AssertionError):
+            serializer.data
 
     def test_partial_validation(self):
         serializer = self.Serializer(data={'char': 'abc'}, partial=True)
@@ -208,11 +210,12 @@ class TestSerializer:
 
             serializer = ExampleSerializer(data=data)
             assert not serializer.is_valid()
-            assert serializer.data == data
             assert serializer.validated_data == {}
             assert serializer.errors == {'char': [
                 exceptions.ErrorDetail(string='Raised error', code='invalid')
             ]}
+            with pytest.raises(AssertionError):
+                serializer.data
 
 
 class TestValidateMethod: