如何在 MongoDB 中进行嵌套的 $lookup 搜索？

Question

我有 3 个收藏：

1. 职位：

+------------------+----------+------ ----------------+ | position_id | company_id |位置名 | +------------------+----------+------ ----------------+ | 1 | 1 |位置 1 | +------------------+----------+------ ----------------+ | 2 | 2 |位置 2 | +------------------+----------+------ ----------------+

1. 公司：

+------------------+----------+------ ----------------+ | company_id |行业ID |公司名称 | +------------------+----------+------ ----------------+ | 1 | 1 |公司 1 | +------------------+----------+------ ----------------+ | 2 | 2 |公司 2 | +-------------------------------------------------- ----------------+

1. 行业：

+------------------+----------+ |行业ID |行业名称 | +------------------+----------+ | 1 |工业1 | +------------------+----------+ | 2 |工业2 | +------------------+----------+

我需要在一个 API 中返回以下结果：

[{
  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：

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 搜索中进行嵌套 $lookup 的正确方法是什么？

提前致谢！

Answer 1

$lookup 3.6 语法允许您连接嵌套表，$unwind 可以从输入文档中解构一个数组字段，从而为每个元素输出一个文档。像这样的

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" }
])

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" }
  }}
])