我有 3 个集合:
- 职位:
+------------------+----------------------+-----------------------+ | position_id | company_id | position_name | +------------------+----------------------+-----------------------+ | 1 | 1 | position 1 | +------------------+----------------------+-----------------------+ | 2 | 2 | position 2 | +------------------+----------------------+-----------------------+
- companies:
+------------------+----------------------+-----------------------+ | company_id | industry_id | company_name | +------------------+----------------------+-----------------------+ | 1 | 1 | company 1 | +------------------+----------------------+-----------------------+ | 2 | 2 | company 2 | +-----------------------------------------------------------------+
- industries:
+------------------+----------------------+ | industry_id | industry_name | +------------------+----------------------+ | 1 | industry 1 | +------------------+----------------------+ | 2 | industry 2 | +------------------+----------------------+
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pipeline部分的代码是这样的:
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 搜索中嵌套 $lookup 的正确方法是什么?
提前致谢!
最佳答案
$lookup
3.6 语法允许您连接嵌套表和 $unwind
从输入文档中解构一个数组字段,为每个元素输出一个文档。像这样
position.aggregate([
{ "$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" }
])
随着 3.4 版本
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" }
}}
])
关于mongodb - 如何在 MongoDB 中进行嵌套 $lookup 搜索?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/52712240/