英文:
How to lookup through an Array in MongoDB and Project Names From a Certain Collection
问题
我有两个集合，一个叫做Exports，另一个叫做Service。在Exports集合中有一个对象，其中包含一个servicesIds数组。
我想要聚合和查找Exports集合中与Service集合匹配的_id，以查找服务的名称。
两个集合中每个文档的结构如下：
Exports:
{
"_id" : "818a2c4fc4",
"companyId" : "7feb1812d8",
"filter" : {
"servicesIds" : [
"0111138dc679d",
"0c18c499435e9",
],
},
"_created_at" : ISODate("2019-10-27T09:06:03.102+0000"),
"_updated_at" : ISODate("2019-10-27T09:06:05.099+0000"),
}
Service:
{
"_id" : "0111138dc679d",
"name" : "Bay Services",
"character" : "B",
"company" : {
"id" : "f718a1c385",
"name" : "xxx"
},
"active" : true,
"tags" : [
],
"_created_at" : ISODate("2020-04-09T06:36:14.442+0000"),
"_updated_at" : ISODate("2020-06-06T03:52:16.770+0000"),
}
我该如何做到这一点？
这是我尝试过的，但它一直给我一个错误：
Mongo服务器错误'$in需要一个数组作为第二个参数，找到：missing'。
这是我的代码：
db.getCollection("Exports").aggregate([
{
"$match": { "companyId": "818a2c4fc4" },
},
{
"$lookup": {
"from": "Service",
"let": { id: "$_id" },
"pipeline": [
{
"$match": {
"$expr": {
"$in": ["$$id", "$filter.servicesIds"]
}
}
}
],
"as": "services"
}
},
])
（注意：由于您要求不翻译代码部分，我提供的是代码的直译翻译。）
英文:
I have two collections, one named Exports and one named Service. Inside the Exports collection there is an object that holds inside of it an array of servicesIds.
I want to aggregate and lookup for the corressponding matching _ids from the Exports collection with the Service collection to find the name of the services.
The structure of the each document for the two collection is as follows:
Exports:
{
"_id" : "818a2c4fc4",
"companyId" : "7feb1812d8",
"filter" : {
"servicesIds" : [
"0111138dc679d",
"0c18c499435e9",
],
},
"_created_at" : ISODate("2019-10-27T09:06:03.102+0000"),
"_updated_at" : ISODate("2019-10-27T09:06:05.099+0000"),
}
Service:
An example of one document with its _id is a foreign key inside the filters object then inside the servicesIds array
{
"_id" : "0111138dc679d",
"name" : "Bay Services",
"character" : "B",
"company" : {
"id" : "f718a1c385",
"name" : "xxx"
},
"active" : true,
"tags" : [
],
"_created_at" : ISODate("2020-04-09T06:36:14.442+0000"),
"_updated_at" : ISODate("2020-06-06T03:52:16.770+0000"),
}
How can i do that?
Here is what i tried, but it keeps giving me and error reading
Mongo Server error '$in requires an array as a second argument, found: missing' on server
Here is my code:
db.getCollection("Exports").aggregate([
{
"$match": { "companyId":"818a2c4fc4" },
},
{
"$lookup": {
"from": "Service",
"let":{ id : "$_id" },
"pipeline": [
{
"$match":
{
"$expr":
{
"$in": ["$$id","$filter.servicesIds"]
}
}
}
],
"as":"services"
}
},
])
答案1
得分: 1
`$unwind` 首先展开数组，或者您可以编辑您的答案，提供您期望的结果，然后我会更正我的答案。
db.Exports.aggregate([
{
"$match": {
"companyId": "7feb1812d8"
}
},
{
"$unwind": "$filter.servicesIds"
},
{
"$lookup": {
"from": "Service",
"localField": "filter.servicesIds",
"foreignField": "_id",
"as": "docs"
}
}
])
https://mongoplayground.net/p/l2VweVYz1Fy
英文:
$unwind the array first, or you can edit your answer with an expected result you want, then I will correct my answer.
db.Exports.aggregate([
{
"$match": {
"companyId": "7feb1812d8"
}
},
{
"$unwind": "$filter.servicesIds"
},
{
"$lookup": {
"from": "Service",
"localField": "filter.servicesIds",
"foreignField": "_id",
"as": "docs"
}
}
])
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