在聚合投影MongoDB中将多个子文档合并为数组

本文介绍了在聚合投影MongoDB中将多个子文档合并为数组的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我在这里试图做的是查询和合并多个子文档，以数组作为回报。我认为聚合框架是可行的方法，但我似乎无法完全正确。

What I am trying to do here is querying and merging multiple sub-documents in return as an array. I think the aggregation framework is the way to go, but I can't seem to get it exactly right.

这里是我的收藏集，名为 visitors ：

Here is my collection called visitors:

{ "_id": ObjectId("57dc5c2b7463d336ec3fff8c"), "username": "Bob", "fullname": "Bobby", "activities": { "visits" : [ { "_id": ObjectId("57dc674e4208b12fd4a52a3d"), "date": ISODate("2016-09-18T08:00:00.000Z"), "location" : "Jakarta", }, { "_id": ObjectId("57dd3795c13c5e2b7484ea4b"), "date": ISODate("2016-09-17T08:00:00.000Z"), "location" : "Denpasar", } ], "purchases" : [ { "_id": ObjectId("57dc4769c0f09317282b3f92"), "date": ISODate("2016-09-17T07:30:00.000Z"), "product_name" : "Shirt", "price": 125000 },{ "_id": ObjectId("57dbfdc6be9dcf1e7c4a1751"), "date": ISODate("2016-09-18T08:30:00.000Z"), "product_name" : "Shoes", "price": 150000 } ]}, } }

这是我想要的文档，并尝试通过聚合实现，这是这样的，条件是我可以按日期排序，使用 limit 和 skip 。

And here is the document that I want and try to achieve with aggregation is this, with condition that i can sort them by date, use limit and skip.

{ "_id": ObjectId("57dc5c2b7463d336ec3fff8c"), "activities": [ { "activity_type": "purchases", "_id": ObjectId("57dbfdc6be9dcf1e7c4a1751"), "date": ISODate("2016-09-18T08:30:00.000Z"), "product_name" : "Shoes", "price": 150000 },{ "activity_type": "visits", "visits_id": ObjectId("57dc674e4208b12fd4a52a3d"), "date": ISODate("2016-09-18T08:00:00.000Z"), "location" : "Jakarta", },{ "activity_type": "visits", "visits_id": ObjectId("57dd3795c13c5e2b7484ea4b"), "date": ISODate("2016-09-17T08:00:00.000Z"), "location" : "Denpasar", },{ "activity_type": "purchases", "date": ISODate("2016-09-17T07:30:00.000Z"), "product_name" : "Shirt", "price": 125000 }] }

我一直在尝试使用此聚合

I've been trying to do this with this aggregation

db.visitors.aggregate([{ $match: { _id: ObjectId("57dc5c2b7463d336ec3fff8c") } }, { $group: { _id: "$_id", visits: { "$addToSet": "$activities.visits" }, purchases: { "$addToSet": "$activities.purchases" } } }])

但是我不明白y我想要的是，而是按其类型对它们进行分组，而我什至不能使用 skip 和 limit （似乎只是跳过并限制访问者人数）。

But I don't get exactly what i want, it was instead just group them by their type, and I can't even use skip and limit (seems to just skip and limit visitors number).

{ "_id": ObjectId("57dc5c2b7463d336ec3fff8c"), "visits": [ [ { "_id": ObjectId("57dc674e4208b12fd4a52a3d"), "date": ISODate("2016-09-18T08:00:00.000Z"), "location" : "Jakarta", }, { "_id": ObjectId("57dd3795c13c5e2b7484ea4b"), "date": ISODate("2016-09-17T08:00:00.000Z"), "location" : "Denpasar", } ] ], "news": [ [ { "_id": ObjectId("57dc4769c0f09317282b3f92"), "date": ISODate("2016-09-17T07:30:00.000Z"), "product_name" : "Shirt", "price": 125000 },{ "_id": ObjectId("57dbfdc6be9dcf1e7c4a1751"), "date": ISODate("2016-09-18T08:30:00.000Z"), "product_name" : "Shoes", "price": 150000 } ] ] }

尝试使用展开，

db.visitors.aggregate([ { $match: { _id: ObjectId("57dc5c2b7463d336ec3fff8c") } }, { $unwind: '$activities.visits' }, { $unwind: '$activities.purchases' }, { $project: { _id: 0, //visits "visits_id": "$activities.visits._id", "visits_date": "$activities.visits.date", "visits_location" : "$activities.visits.location" //purchases "purchases_id": "$activities.purchases._id", "purchases_date": "$activities.purchases.date", "purchases_product_name": "$activities.purchases.product_name", "purchases_price": "$activities.purchases.price", } } ]) .skip(0) .limit(2)

但似乎在每个索引处合并了不同类型的文档

but it seems to merge the documents with different type at each index

{ "_id": ObjectId("57dc5c2b7463d336ec3fff8c"), "activities": [ { "purchases_id": ObjectId("57dbfdc6be9dcf1e7c4a1751"), "purchases_date": ISODate("2016-09-18T08:30:00.000Z"), "purchases_product_name" : "Shoes", "purchases_price": 150000 "visits_id": ObjectId("57dc674e4208b12fd4a52a3d"), "visits_date": ISODate("2016-09-18T08:00:00.000Z"), "visits_location" : "Jakarta", },{ "purchases_id": ObjectId("57dc4769c0f09317282b3f92"), "purchases_date": ISODate("2016-09-17T07:30:00.000Z"), "purchases_product_name" : "Shirt", "purchases_price": 125000 "visits_id": ObjectId("57dd3795c13c5e2b7484ea4b"), "visits_date": ISODate("2016-09-17T08:00:00.000Z"), "visits_location" : "Denpasar", }] }

是否可以对当前文档执行此操作？还是应该更改文档结构？

Is it possible to do this with my current document? Or should I change my document structure?

更新已解决

我结束了在数组中的每个子文档中添加 activity_type ，并使用 $ setUnion 合并多个数组作为数组来解决此问题，并使用 $ slice 限制和跳过数组。我不知道如何，但是似乎 $ setUnion 已经自动对其进行了排序

I ended up add activity_type at each of my subdocument in array, and solve this using $setUnion to merge multiple array as an array, and use $slice to limit and skip the array. I don't know how, but it seems $setUnion already sorting it automatically

db.visitors.aggregate([ { $project: { activities: { $setUnion: ['$activities.visits', '$activities.purchases'], } } }, { $project:{ activites: { $slice: ["$activities", 0, 2] } } } ])

推荐答案

如果将 activity_type 字段添加到每个数组元素中，则容易使用 $ setUnion 和一个 aggregation 阶段：

If you add activity_type field to each of the array elements, it will be easy to use $setUnion with one aggregation stage:

db.visitors.aggregate([ { $project: { activities: { $setUnion: ['$activities.visits', '$activities.purchases'] } } } ])

在这种情况下，您将获得连接的数组

In this case you will get the arrays "concatenated" together into one activities array with their type.

对于问题的另一部分， sort ，跳过（限制）是聚合阶段，将对每个文档而不是子文档起作用，因此您需要 $ match 您所需的文档， $ unwind 结果活动数组从以前开始，然后您就可以使用所有 sort ， skip ， limit 运算符。

For the other part of your question, sort, skip, limit, are aggregation stages that will work on each document and not sub-documents, so you will need to $match your needed document, $unwind the result activities array from before, and then you can can use all of the sort, skip, limit operators.