Improvement on error returned by ListSerializer

[shinneider]

Hi,

I suggest improvement on errors on ListSerializer.

currently the errors of ListSerializer is very bad for error revision.
if i send a list of data, their return only data with errors, ex:

[
  {"data": "success example", "obj": 1},
  {"data": "error example", "obj": 2}
]
# return
[
  {},
  {"data" : ["invalid data"]}
]

if i need to get data with error, it's necessary to keep sended data, and compare to received error data.
it's very poor for send a lot of data and get errors in data.

my suggestion is improve this to:

[
  {
     "sended": {"data": "success example", "obj": 1},
     "errors": []
  },
  {
    "sended": {"data": "error example", "obj": 2},
    "errors" {"data" : ["invalid data"]}
  }
]

# or just return errors
[
  {
    "sended": {"data": "error example", "obj": 2},
    "errors" {"data" : ["invalid data"]}
  }
]

Because this return sended data, and allow to check errors just in the response, no need to keep sended data.

just changing rest_framework/serializers.py::ListSerializer:

def to_internal_value(self, data):
   ...
   ret = []
   errors = []

   for item in data:
      try:
         validated = self.child.run_validation(item)
      except ValidationError as exc:
         errors.append(exc.detail)
      else:
         ret.append(validated)
         errors.append({})

   if any(errors):
      raise ValidationError(errors)

   return ret

to

def to_internal_value(self, data):
   ...
   ret = []
   errors_map = []
   has_error = False

   for item in data:
      try:
         validated = self.child.run_validation(item)
      except ValidationError as exc:
         has_error = True
         errors_map.append({"sended": item, "errors": exc.detail})
      else:
         ret.append(validated)
         errors_map.append({"sended": item, "errors": []}) # if return errors data only, remove this line

   if has_error:
      raise ValidationError(errors_map)

   return ret