如何在猫鼬中聚合嵌套查找数组？答案

【问题标题】：How to aggregate nested lookup array in mongoose?如何在猫鼬中聚合嵌套查找数组？
【发布时间】：2021-05-06 13:22:09
【问题描述】：

我对如何查找嵌套数组有疑问，例如我有 4 个集合。

用户收藏

"user": [
    {
      "_id": "1234",
      "name": "Tony",
      "language": [
        {
          "_id": "111",
          "language_id": "919",
          "level": "Expert"
        },
        {
          "_id": "111",
          "language_id": "920",
          "level": "Basic"
        }
      ]
    }
  ]

语言合集

"language": [
    {
      "_id": "919",
      "name": "English"
    },
    {
      "_id": "920",
      "name": "Chinese"
    }
  ]

工作

"job": [
    {
      "_id": "10",
      "title": "Programmer",
      "location": "New York"
    }
  ],

简历提交收藏

"cvsubmit": [
    {
      "_id": "11",
      "id_user": "1234",
      "id_job": "11"
    }
  ]

我的查询聚合是：

db.cvsubmit.aggregate([
  {
    $lookup: {
      from: "user",
      localField: "id_user",
      foreignField: "_id",
      as: "id_user"
    }
  },
  {
    $lookup: {
      from: "language",
      localField: "id_user.language.language_id",
      foreignField: "_id",
      as: "id_user.language.language_id"
    }
  },
])

但结果是：

[
  {
    "_id": "11",
    "id_job": "11",
    "id_user": {
      "language": {
        "language_id": [
          {
            "_id": "919",
            "name": "English"
          },
          {
            "_id": "920",
            "name": "Chinese"
          }
        ]
      }
    }
  }
]

我想要这样的结果，还显示所有用户数据详细信息，如name：

[
  {
    "_id": "11",
    "id_job": "11",
    "id_user": {
      "_id": "1234",
      "name": "Tony"
      "language": [
          {
            "_id": "919",
            "name": "English",
            "Level": "Expert"
          },
          {
            "_id": "920",
            "name": "Chinese",
            "level": "Basic"
          }
        ]
    }
  }
]

Mongo Playground 链接https://mongoplayground.net/p/i0yCucjruey

之前谢谢。

【问题讨论】：

标签： mongodb mongoose aggregation-framework

【解决方案1】：

$lookup 与 user 合集
$unwind解构id_user数组
$lookup 与 language 集合并在 languages 字段中返回
$map 迭代 id_user.language 数组的外观
$reduce 迭代从集合返回的 languages 数组的循环，检查条件如果 language_id 匹配则返回 name

db.cvsubmit.aggregate([
  {
    $lookup: {
      from: "user",
      localField: "id_user",
      foreignField: "_id",
      as: "id_user"
    }
  },
  { $unwind: "$id_user" },
  {
    $lookup: {
      from: "language",
      localField: "id_user.language.language_id",
      foreignField: "_id",
      as: "languages"
    }
  },
  {
    $addFields: {
      languages: "$$REMOVE",
      "id_user.language": {
        $map: {
          input: "$id_user.language",
          as: "l",
          in: {
            _id: "$$l._id",
            level: "$$l.level",
            name: {
              $reduce: {
                input: "$languages",
                initialValue: "",
                in: {
                  $cond: [
                    { $eq: ["$$this._id", "$$l.language_id"] },
                    "$$this.name",
                    "$$value"
                  ]
                }
              }
            }
          }
        }
      }
    }
  }
])

Playground

根据 NoSQL，您的数据库结构不准确，最多应该有 2 个集合，使用 $lookup 和 $unwind 进行连接的战利品会导致性能问题。

【讨论】：