code: def _link_rels(obj, fields=None, save=False, overwrite=False):
      
      if not fields:
          meta = obj._meta
          fields = [f.name for f in meta.fields if hasattr(f, 'do_related_class') and not f.primary_key and hasattr(meta, '_get_' + f.name) and hasattr(meta, '_' + f.name)]
      for field in fields:
          # skip fields if they contain non-null data and `overwrite` option wasn't set
          if not overwrite and not isinstance(getattr(obj, field, None), NoneType):
              # print 'skipping %s which already has a value of %s' % (field, getattr(obj, field, None))
              continue
          if hasattr(obj, field):
              setattr(obj, field, getattr(obj, '_' + field, None))
      if save:
          obj.save()
      return obj
docs: Populate any database related fields (ForeignKeyField, OneToOneField) that have `_get`ters to populate them with