如何在MongoDB中嵌套$ lookup搜索? [英] How to do nested $lookup search in MongoDB?
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问题描述
我有3个收藏集:
- 职位:
+------------------+----------------------+-----------------------+
| position_id | company_id | position_name |
+------------------+----------------------+-----------------------+
| 1 | 1 | position 1 |
+------------------+----------------------+-----------------------+
| 2 | 2 | position 2 |
+------------------+----------------------+-----------------------+
- 公司:
+------------------+----------------------+-----------------------+
| company_id | industry_id | company_name |
+------------------+----------------------+-----------------------+
| 1 | 1 | company 1 |
+------------------+----------------------+-----------------------+
| 2 | 2 | company 2 |
+-----------------------------------------------------------------+
- 行业:
+------------------+----------------------+
| industry_id | industry_name |
+------------------+----------------------+
| 1 | industry 1 |
+------------------+----------------------+
| 2 | industry 2 |
+------------------+----------------------+
我需要在一个API中返回以下结果:
I need to return the following result in one API:
[{
position_id: 1,
position_name: 'position 1',
company: {
company_id: 1,
company_name: 'company 1',
industry: {
industry_id: 1,
industry_name: 'industry 1',
}
}
}, {
position_id: 2,
posiiton_name: 'position 2',
company: {
company_id: 2,
company_name: 'company 2',
industry: {
industry_id: 2,
industry_name: 'industry 2',
}
}
}]
所以我能想到的管道部分的代码如下:
So the code of the pipeline part I can think of is like the following:
const pipelines = [{
$lookup: {
from: 'companies',
localField: 'company_id',
foreignField: 'company_id',
as: 'company',
$lookup: {
from: 'industries',
localField: 'industry_id',
foreignField: 'industry_id',
as: 'industry'
}
}
}]
return positions.aggregate(pipelines);
但这会引发一些错误.那么在mongodb搜索中执行嵌套$ lookup的正确方法是什么?
But this would throw some errors. So what is the correct way to do the nested $lookup in mongodb search?
提前谢谢!
推荐答案
"> $unwind
可以将数组字段从输入文档分解为输出每个元素的文档.像这样
$lookup
3.6 syntax allows you to join nested tables and $unwind
to deconstructs an array field from the input documents to output a document for each element. Something like this
position.aggregate([
{ "$lookup": {
"from": "companies",
"let": { "companyId": "$company_id" },
"pipeline": [
{ "$match": { "$expr": { "$eq": [ "$_id", "$$companyId" ] } } },
{ "$lookup": {
"from": "industries",
"let": { "industry_id": "$industry_id" },
"pipeline": [
{ "$match": { "$expr": { "$eq": [ "$_id", "$$industry_id" ] } } }
],
"as": "industry"
}},
{ "$unwind": "$industry" }
],
"as": "company"
}},
{ "$unwind": "$company" }
])
使用3.4版
position.aggregate([
{ "$lookup": {
"from": "companies",
"localField": "company_id",
"foreignField": "_id",
"as": "companies"
}},
{ "$unwind": "$companies" },
{ "$lookup": {
"from": "industries",
"localField": "companies.industry_id",
"foreignField": "_id",
"as": "companies.industry"
}},
{ "$unwind": "$companies.industry" },
{ "$group": {
"_id": "$_id",
"companies": { "$push": "$companies" }
}}
])
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