填写记录中的缺失日期 [英] Fill missing dates in records

问题描述

我有一个ProductViews的集合.

产品视图

{
    productId: '5b8c0f3204a10228b00a1745,
    createdAt: '2018-09-07T17:18:40.759Z',
}

我有一个查询，用于获取特定产品的每日视图.

And I have a query for fetching the daily views for a specific product.

查询

ProductView.aggregate([
    { $match: { productId } },
    { $project: { day: { $substr: ["$createdAt", 0, 10] } } },
    {
        $group: {
            _id: "$day",
            count: { $sum: 1 },
            time: { $avg: "$createdAt" },
        }
    },
    { $sort: { _id: 1 } },
    {
        $project: {
            date: '$_id',
            views: '$count',
        },
    },
]).exec((err, result) => ...)

当前结果

[
    { date: '2018-09-01', views: 1 },
    { date: '2018-09-02', views: 3 },
    { date: '2018-09-04', views: 2 },
    { date: '2018-09-05', views: 5 },
    // ...
]

问题

问题在于，这种聚合在具有0视图的天内不会返回{ date: '2018-09-03', views: 0 }.这将导致数据显示不正确:

The issue is, that this aggregation does not return { date: '2018-09-03', views: 0 } for days with 0 views. This results in incorrect displaying of the data:

结果应类似于

[
    { date: '2018-09-01', views: 1 },
    { date: '2018-09-02', views: 3 },
    { date: '2018-09-03', views: 0 },
    { date: '2018-09-04', views: 2 },
    { date: '2018-09-05', views: 5 },
    // ...
]

P.S .:最好输入开始日期和结束日期以根据此范围输出结果

P.S.: It would be perfect to pass in the start and end dates to output results based on this range

推荐答案

您需要几个附加步骤来返回默认值.首先，您需要使用$group，将_id设置为null，以将所有结果收集到一个文档中.然后，您可以将 $ map 使用几天作为输入.在该$map内部，您可以使用 $ indexOfArray 来查找该日期是否存在于您当前的结果集中.如果是(index != -1)，则可以返回该值，否则需要返回默认子文档，其中views设置为0.然后，您可以使用 $ unwind 返回列表文档和 $ replaceRoot 来促进嵌套stats达到最高水平.

You need few additional stages to return default values. First of all you need to use $group with _id set to null to collect all results in one document. Then you can use $map with an array of days as an input. Inside that $map you can use $indexOfArray to find if that date exists in your current result set. If yes (index != -1) then you can return that value, otherwise you need to return default subdocument with views set to 0. Then you can use $unwind to get back a list of documents and $replaceRoot to promote nested stats to a top level.

ProductView.aggregate([
    { $match: { productId: '5b8c0f3204a10228b00a1745' } },
    { $project: { day: { $substr: ["$createdAt", 0, 10] } } },
    {
        $group: {
            _id: "$day",
            count: { $sum: 1 },
            time: { $avg: "$createdAt" },
        }
    },
    { $sort: { _id: 1 } },
    {
        $project: {
            date: '$_id',
            views: '$count',
        },
    },
    {
        $group: {
            _id: null,
            stats: { $push: "$$ROOT" }
        }
    },
    {
        $project: {
            stats: {
                $map: {
                    input: [ "2018-09-01", "2018-09-02", "2018-09-03", "2018-09-04", "2018-09-05" ],
                    as: "date",
                    in: {
                        $let: {
                            vars: { dateIndex: { "$indexOfArray": [ "$stats._id", "$$date" ] } },
                            in: { 
                                $cond: {
                                    if: { $ne: [ "$$dateIndex", -1 ] },
                                    then: { $arrayElemAt: [ "$stats", "$$dateIndex" ] },
                                    else: { _id: "$$date", date: "$$date", views: 0 }
                                } 
                            }
                        }
                    }
                }
            }
        }
    },
    {
        $unwind: "$stats"
    },
    {
        $replaceRoot: {
            newRoot: "$stats"
        }
    }
]).exec((err, result) => ...)

您可以使用简单循环在应用程序逻辑中生成静态日期列表.我相信在MongoDB中也是可行的(使用 $ range )，但可能会使此聚合管道复杂化.让我知道您是否满意，或者想尝试在MongoDB中生成该日期数组.

You can generate a static list of dates in your application logic using simple loop. I believe that's possible in MongoDB as well (using $range) but it might complicate this aggregation pipeline. Let me know if you're fine with that or you want to try to generate that array of dates in MongoDB.

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