我有一个集合，其中包含客户端报告的一些事件，例如:{"_id":ObjectId("54f43159c922ac0b4387ef9c"),"appversion":"v1.2","appid":"930370913","clkip":"","actip":"","clktime":1425289561,"acttime":0,"platform":"google","isnotified":false,"idfa":"14A900D9-A61A-41DC-A327-96EBE4BA57B31"}{"_id":ObjectId("54f43159c922ac0b4387ef9d"),"a