mongoDb 查找文档中的条目数和按字段区分的条目

Question

我的文档结构是：

[{
    "l": {
    "ln": "Hyderabad",

    },
    "cid": "customer1",
    "created": ISODate("2015-07-20T13:15:45.198        Z")
}, {
    "l": {
    "ln": "Hyderabad",

    },
    "cid": "customer2",
    "created": ISODate("2015-07-20T13:15:45.198        Z")
}, {
    "l": {
    "ln": "Delhi",

    },
    "cid": "customer3",
    "created": ISODate("2015-07-20T13:15:45.198        Z")
}, {
    "l": {
    "ln": "Delhi",

    },
    "cid": "customer3",
    "created": ISODate("2015-07-20T13:15:45.198        Z")
}, {
    "l": {
    "ln": "Bangalore",

    },
    "cid": "customer1",
    "created": ISODate("2015-07-20T13:15:45.198        Z")
}, {
    "l": {
    "ln": "Bangalore",

    },
    "cid": "customer5",
    "created": ISODate("2015-07-20T13:15:45.198        Z")
}, {
    "l": {
    "ln": "Bangalore",

    },
    "cid": "customer6",
    "created": ISODate("2015-07-20T13:15:45.198        Z")
}, {
    "l": {
    "ln": "Bangalore",

    },
    "cid": "customer6",
    "created": ISODate("2015-07-20T13:15:45.198        Z")
}]

我的 o/p 应该是：

[{
    "ln": "Hyderabad",
    "entries": 2,
    "numberofdistinctcustomers": 2,
    "customers": [
    "customer1",
    "customer2"
    ]
} {
    "ln": "Delhi",
    "entries": 2,
    "numberofdistinctcustomers": 1,
    "customers": [
    "customer3"
    ]
} {
    "ln": "Bangalore",
    "entries": 4,
    "numberofdistinctcustomers": 3,
    "customers": [
    "customer1",
    "customer5",
    "customer6"
    ]
}]

有人可以帮我吗？我知道为此我们需要使用 $group by ln 来查找 entries。如何找到不同cids 的数量？

请帮我解决这个问题？

Answer 1

您应该使用aggregation 来获得预期的输出。

首先您需要按l.ln 分组，然后使用$addToSet 获得不同的customers。要获得numberofdistinctcustomers，您可以在投影中使用$size 运算符。

查询将如下所示：

db.collection.aggregate({
    $group: {
    _id: "$l.ln",
    "entries": {
        $sum: 1
    },
    "dis": {
        $addToSet: "$cid"
    }
    }
}, {
    $project: {
    "ln": "$_id",
    "entries": 1,
    "customers": "$dis",
    "numberofdistinctcustomers": {
        "$size": "$dis"
    }
    }
})