code: def _extract_data(self, request):
          
          data = {}
          for field, val in six.iteritems(request.POST):
              if field in self.immutable_fields:
                  continue  # Ignore immutable fields silently.
  
              if field in self.fields:
                  field_obj = self.model._meta.get_field(field)
                  val = self._extract_value(val)
                  if isinstance(field_obj, models.ForeignKey):
                      if field_obj.null and not val:
                          clean_value = None
                      else:
                          clean_value = field_obj.rel.to.objects.get(pk=val)
                  else:
                      clean_value = field_obj.to_python(val)
                  data[smart_str(field)] = clean_value
  
          return data
docs: Extract data from POST.
  
          Handles extracting a vanilla Python dict of values that are present
          in the given model. This also handles instances of ``ForeignKey`` and
          will convert those to the appropriate object instances from the
          database. In other words, it will see that user is a ``ForeignKey`` to
          Django's ``User`` class, assume the value is an appropriate pk, and
          load up that record.