问题描述
我有一个 ProductViews
的集合:
{产品 ID:5b8c0f3204a10228b00a1745",createdAt:2018-09-07T17:18:40.759Z"}
我有一个查询来获取特定产品的每日浏览量:
ProductView.aggregate([{ $match: { productId } },{ $project: { day: { $substr: ["$createdAt", 0, 10] } } },{$组:{_id: "$day",计数: { $sum: 1 },时间:{ $avg: "$createdAt";},}},{ $sort: { _id: 1 } },{$项目:{日期:'$_id',意见:'$count',},},]).exec((错误,结果) => ...)
目前给出:
[{ 日期:'2018-09-01',观看次数:1},{ 日期:'2018-09-02',观看次数:3 },{ 日期:'2018-09-04',观看次数:2 },{ 日期:'2018-09-05',观看次数:5 },//...]问题:
问题是,对于具有 0
视图的天数,此聚合不会返回 { date: '2018-09-03', views: 0 }
.这会导致数据显示不正确:[![enter image description here][1]][1]
结果应如下所示:
[{ 日期:'2018-09-01',观看次数:1},{ 日期:'2018-09-02',观看次数:3 },{ 日期:'2018-09-03',观看次数:0 },<={ 日期:'2018-09-04',观看次数:2 },{ 日期:'2018-09-05',观看次数:5 },//...]P.S.:最好是传入开始日期和结束日期来输出基于这个范围的结果[1]:https://i.stack.imgur.com/uHPBs.png
您需要几个额外的阶段来返回默认值.首先,您需要使用 $group
并将 _id
设置为 null
以将所有结果收集到一个文档中.然后你可以使用 $map 和一组天数作为输入.在那个 $map
里面你可以使用 $indexOfArray 以查找当前结果集中是否存在该日期.如果是 (index != -1
) 那么你可以返回那个值,否则你需要返回默认的子文档,views
设置为 0
.然后你可以使用 $unwind 来获取列表文档和 $replaceRoot 以促进嵌套 统计数据
到顶级.
ProductView.aggregate([{ $match: { productId: '5b8c0f3204a10228b00a1745' } },{ $project: { day: { $substr: ["$createdAt", 0, 10] } } },{$组:{_id: "$day",计数: { $sum: 1 },时间:{ $avg: "$createdAt" },}},{ $sort: { _id: 1 } },{$项目:{日期:'$_id',意见:'$count',},},{$组:{_id:空,统计信息:{ $push: "$$ROOT" }}},{$项目:{统计:{$地图:{输入:[ "2018-09-01", "2018-09-02", "2018-09-03", "2018-09-04", "2018-09-05" ],如:日期",在: {$let: {vars: { dateIndex: { "$indexOfArray": [ "$stats._id", "$$date" ] } },在: {$cond: {如果:{ $ne: [ "$$dateIndex", -1 ] },然后:{ $arrayElemAt: [ "$stats", "$$dateIndex" ] },其他:{_id:$$date",日期:$$date",视图:0}}}}}}}}},{$unwind: "$stats"},{$替换根:{newRoot: "$stats"}}]).exec((错误,结果) => ...)
您可以使用简单的循环在应用程序逻辑中生成静态日期列表.我相信这在 MongoDB 中也是可能的(使用 $range) 但它可能会使这个聚合管道复杂化.如果您对此感到满意,或者您想尝试在 MongoDB 中生成该日期数组,请告诉我.
I have a collection of ProductViews
:
{
productId: "5b8c0f3204a10228b00a1745",
createdAt: "2018-09-07T17:18:40.759Z"
}
And I have a query for fetching the daily views for a specific product:
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) => ...)
which currently gives:
[
{ date: '2018-09-01', views: 1 },
{ date: '2018-09-02', views: 3 },
{ date: '2018-09-04', views: 2 },
{ date: '2018-09-05', views: 5 },
// ...
]
Issue:
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: [![enter image description here][1]][1]
Results should look like:
[
{ 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.: It would be perfect to pass in the start and end dates to output results based on this range[1]: https://i.stack.imgur.com/uHPBs.png
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) => ...)
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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