MongoDB：按照标准对文档进行分组

Question

我正在使用Mongo 2.4。我有这个：

{ 
    "_id" : ObjectId(), 
    "place" : "52f06eb4a0a9210c11000032", 
    "message" : "Hi" 
} 
{ 
    "_id" : ObjectId(), 
    "place" : "52f06eb4a0a9210c11000032", 
    "message" : "Hi, how are you?" 
} 
{ 
    "_id" : ObjectId(), 
    "place" : "32f06eb4a0a9210c11000032", 
    "message" : "?" 
} 

我需要任何方法来按“地点”对文档进行分组。说得通？

Answer 1

db.collection.aggregate(
    { 
    $group: { 
     _id: "$place", 
     messages: { $push: "$message" } 
    } 
    } 
) 

例如，从MongoDB的文档导出：http://docs.mongodb.org/manual/reference/operator/aggregation/push/#grp._S_push