docs: def validate(cls, mapper_spec):
      """Inherit docs."""
      super(DatastoreInputReader, cls).validate(mapper_spec)
      params = _get_params(mapper_spec)
      entity_kind = params[cls.ENTITY_KIND_PARAM]
      # Fail fast if Model cannot be located.
      try:
        model_class = util.for_name(entity_kind)
      except ImportError, e:
        raise BadReaderParamsError("Bad entity kind: %s" % e)
      if cls.FILTERS_PARAM in params:
        filters = params[cls.FILTERS_PARAM]
        if issubclass(model_class, db.Model):
          cls._validate_filters(filters, model_class)
        else:
          cls._validate_filters_ndb(filters, model_class)
        property_range.PropertyRange(filters, entity_kind)