'Create new DatastoreInputReader from the json, encoded by to_json.
Args:
json: json map representation of DatastoreInputReader.
Returns:
an instance of DatastoreInputReader with all data deserialized from json.'

@classmethod
def from_json(cls, json):

    query_range = cls(json[cls.ENTITY_KIND_PARAM], key_range.KeyRange.from_json(json[cls.KEY_RANGE_PARAM]), json[cls.MAPPER_PARAMS])
    return query_range
