MongoDB聚合始終返回0值

Question

以下查詢：

[{
            $match: {
                $and: [
                    {campaignID: "12345"},
                    {date: "2016-10-18"},
                    {hour: {$gte: 0}},
                    {hour: {$lte: 3}}
                ]
            }
        }
}]

返回以下（正確）數據：

[{"_id":"580638b1e4b01c1a027e82c1","campaignID":"12345","date":"2016-10-18",
"hour":0,"foo":10,"bar":10},
{"_id":"580638cbe4b01c1a027e82c2","campaignID":"12345","date":"2016-10-18",
"hour":1,"foo":11,"bar":11},
{"_id":"580638e5e4b01c1a027e82c3","campaignID":"12345","date":"2016-10-18",
"hour":2,"foo":12,"bar":12},
{"_id":"580638efe4b01c1a027e82c4","campaignID":"12345","date":"2016-10-18",
"hour":3,"foo":13,"bar":13}]

但是下面的查詢：

[
        {
            $match: {
                $and: [
                    {campaignID: "12345"},
                    {date: "2016-10-18"},
                    {hour: {$gte: 0}},
                    {hour: {$lte: 3}}
                ]
            }
        },
        {
            $group: {
                _id: campaignID,
                foo:{$sum: "foo"},
                bar:{$sum: "bar"}
            }
        }
]

返回以下（錯誤）數據：

[{"_id":"sA48VsoQyuuEDVI5lr4loL31mqoCRT","foo":0,"bar":0}]

'foo'和'bar'都應該是46（10 + 11 + 12 + 13）

我究竟做錯了什么？

Answer 1

您應該在字段名稱中使用$來引用其值。

$group: {
    _id: "$campaignID",
    foo:{$sum: "$foo"},
    bar:{$sum: "$bar"}
}