MongoDB的聚合框架和Python

Question

我的下一个集合：

{"status": "new", "date": {"$date": 1334841845571}, "_id": {"$oid": "4f901223e4b0c2899fb22da0"}, "description": "description 1", "number": "01"} 
{"status": "new", "date": {"$date": 1334841845571}, "_id": {"$oid": "4f90126fe4b0c2899fb22da1"}, "description": "description 1", "number": "02"} 
{"status": "new", "date": {"$date": 1334841845571}, "_id": {"$oid": "4f901276e4b0c2899fb22da2"}, "description": "description 1", "number": "03"} 
{"status": "blocked", "date": {"$date": 1332163445571}, "_id": {"$oid": "4f901286e4b0c2899fb22da3"}, "description": "description 1", "number": "04"} 
{"status": "blocked", "date": {"$date": 1332163445571}, "_id": {"$oid": "4f90128ee4b0c2899fb22da4"}, "description": "description 1", "number": "05"} 
{"status": "blocked", "date": {"$date": 1332163445571}, "_id": {"$oid": "4f901292e4b0c2899fb22da5"}, "description": "description 1", "number": "06"} 

我想按 '状态' 栏：

cursor = db.command('aggregate', table, pipeline=[ 
      {'$project': {u'date': 1, u'status': 1, u'number': 1, u'description': 1}} 
      {'$group': {'_id': u'$status'}}]) 

但我得到这个：

"ok" 
"result" 

为什么？

Answer 1

您将需要这些额外的字段在您的管道添加到“$组”命令，但你需要指定group命令应该如何对其进行聚合，因为它不能只是把它们都在同一个阵列。请提供您期望的输出。