Question

我想在输出中投射'VBID'字段。但是，即使我在$ project中包含'VBID'字段，我也没有得到所需的输出。我错过了什么吗？

db.VehicleCount.aggregate([
    {"$match":  {   "VBID" : "SL0008",
                    "Tstmp" : {"$gte" : 1506970800000}
                }
    },
    {"$group":  {   "_id": {"$divide" : [{ "$subtract" : [{"$divide" : ["$Tstmp", 1000]}, { "$mod" : [{"$divide" : ["$Tstmp", 1000]}, 3600] }] }, 3600 ]}, 
                    "Car": {"$sum" : {"$cond": [ { "$eq": [ "$VType", 0 ] }, 1, 0 ]}},
                    "Large vehicle": {"$sum" : {"$cond": [ { "$eq": [ "$VType", 1 ] }, 1, 0 ]}},
                    "Bike": {"$sum" : {"$cond": [ { "$eq": [ "$VType", 2 ] }, 1, 0 ]}}
                }
    },
    {"$project" : { "_id" : 1,
                    "Timestamp" : {"$multiply": ["$_id", 3600]},
                    "VBID" : 1,
                    "Car" : 1,
                    "Large vehicle" : 1,
                    "Bike" : 1
                }
    },
    {"$sort" :  {   "Timestamp" : 1}}
    ])

由于

Answer 1

您必须在 _id 字段中添加VBID。

db.VehicleCount.aggregate([
    {"$match":  {   "VBID" : "SL0008",
                    "Tstmp" : {"$gte" : 1506970800000}
                }
    },
    {"$group":  {   
        "_id": {val:{"$divide" : [{ "$subtract" : [{"$divide" : ["$Tstmp", 1000]}, { "$mod" : [{"$divide" : ["$Tstmp", 1000]}, 3600] }] }, 3600 ]}
        ,VBID:'$VBID'}, 

                    "Car": {"$sum" : {"$cond": [ { "$eq": [ "$VType", 0 ] }, 1, 0 ]}},
                    "Large vehicle": {"$sum" : {"$cond": [ { "$eq": [ "$VType", 1 ] }, 1, 0 ]}},
                    "Bike": {"$sum" : {"$cond": [ { "$eq": [ "$VType", 2 ] }, 1, 0 ]}}
                }
    },
    {"$project" : { "_id" : 1,
                    "Timestamp" : {"$multiply": ["$_id.val", 3600]},
                    "VBID" : "$_id.VBID",
                    "Car" : 1,
                    "Large vehicle" : 1,
                    "Bike" : 1
                }
    },
    {"$sort" :  {   "Timestamp" : 1}}
    ])

Mongodb项目聚合输出中的$ match字段

1 个答案: