o Sb@sdZddlmZddlmZddlmZddlmZddl m Z m Z Gddde Z Gd d d e ZGd d d eZGd dde ZdS)z;Perform aggregation operations on a collection or database.)SON)common)validate_collation_or_none)ConfigurationError)ReadPreference _AggWritePrefc@s^eZdZdZ    dddZeddZeddZd d Zed d Z d dZ ddZ dS)_AggregationCommandzThe internal abstract base class for aggregation cursors. Should not be called directly by application developers. Use :meth:`pymongo.collection.Collection.aggregate`, or :meth:`pymongo.database.Database.aggregate` instead. Nc Csd|vrtd||_td|}||_d|_|r(d|dvs%d|dvr(d|_td ||durs