title: django rest framework search filter all fields
body: <p>I have a base model view set which i can handle order, pagination and search functionalities.
  When i have proper filter backends, i can set ordering_fields, search_fields but my question is that:
   like i can set <code>ordering_fields = '__all__'</code>  isn't it possible to set search_fields for all?</p>
  
  <p>I've looked for deep inside filtering mechanism and came here:</p>
  
  <pre><code>def filter_queryset(self, request, queryset, view):
      search_fields = getattr(view, 'search_fields', None)
  
      if not search_fields:
          return queryset
  
      orm_lookups = [self.construct_search(six.text_type(search_field))
                     for search_field in search_fields]
  
      for search_term in self.get_search_terms(request):
          or_queries = [models.Q(**{orm_lookup: search_term})
                        for orm_lookup in orm_lookups]
          queryset = queryset.filter(reduce(operator.or_, or_queries))
  
      return queryset
  </code></pre>
  
  <p>drf fails on generate search_fields if it is set <code>search_fields='__all__'</code>
  Is there any other way to provide search by all functionality?</p>