如何从MongoDB单文档生成多文档？附嵌套数组过滤条件

需求说明 #

• 针对包含cars嵌套数组的MongoDB文档，需完成以下查询操作：
  1. 筛选出cars数组中存在status: "inprogress"且parent_company: true对象的组；
  2. 每个组（按parent_company_id划分）内至少有一个cars对象的model数组包含"v12"；
  3. 将同一parent_company_id对应的所有cars对象打包为独立文档，保留原文档的_id、name等顶层字段。

数据库示例文档 #

{
  "_id" : ObjectId("63a8808652f40e1d48a3d1d7"),
  "name" : "A",
  "description" : null,
  "cars" : [
    {
      "id" : "63a8808c52f40e1d48a3d1da",
      "owner" : "John Doe",
      "purchase_date" : "2022-12-25",
      "status" : "inprogress",
      "parent_company" : true,
      "parent_company_id" : "63a8808c52f40e1d48a3d1da",
      "model" : []
    },
    {
      "id" : "63a880a552f40e1d48a3d1dc",
      "owner" : "John Doe 1",
      "purchase_date" : "2022-12-25",
      "parent_company" : false,
      "parent_company_id" : "63a8808c52f40e1d48a3d1da",
      "model" : ["v12"]
    },
    {
      "id" : "63a880f752f40e1d48assddd",
      "owner" : "John Doe 1",
      "purchase_date" : "2022-12-25",
      "parent_company" : false,
      "parent_company_id" : "63a8808c52f40e1d48a3d1da",
      "model" : []
    },
    {
      "id" : "63a880f752f40e1d48a3d207",
      "owner" : "John Doe 11",
      "dt" : "2022-12-25",
      "status" : "inprogress",
      "parent_company" : true,
      "parent_company_id" : "63a880f752f40e1d48a3d207",
      "model" : ["v12"]
    },
    {
      "id" : "63a880f752f40e1d48agfddd",
      "owner" : "John Doe 112",
      "dt" : "2022-12-25",
      "status" : "inprogress",
      "parent_company" : true,
      "parent_company_id" : "63a880f752f40e1d48agfddd",
      "model" : []
    }
  ]
}

预期查询结果 #

[
  {
    "_id" : ObjectId("63a8808652f40e1d48a3d1d7"),
    "name" : "A",
    "description" : null,
    "cars" : [
      {
        "id" : "63a8808c52f40e1d48a3d1da",
        "owner" : "John Doe",
        "purchase_date" : "2022-12-25",
        "status" : "inprogress",
        "parent_company" : true,
        "parent_company_id" : "63a8808c52f40e1d48a3d1da",
        "model" : []
      },
      {
        "id" : "63a880a552f40e1d48a3d1dc",
        "owner" : "John Doe 1",
        "purchase_date" : "2022-12-25",
        "parent_company" : false,
        "parent_company_id" : "63a8808c52f40e1d48a3d1da",
        "model" : ["v12"]
      },
      {
        "id" : "63a880f752f40e1d48assddd",
        "owner" : "John Doe 1",
        "purchase_date" : "2022-12-25",
        "parent_company" : false,
        "parent_company_id" : "63a8808c52f40e1d48a3d1da",
        "model" : []
      }
    ]
  },
  {
    "_id" : ObjectId("63a8808652f40e1d48a3d1d7"),
    "name" : "A",
    "description" : null,
    "cars" : [
      {
        "id" : "63a880f752f40e1d48a3d207",
        "owner" : "John Doe 11",
        "dt" : "2022-12-25",
        "status" : "inprogress",
        "parent_company" : true,
        "parent_company_id" : "63a880f752f40e1d48a3d207",
        "model" : ["v12"]
      }
    ]
  }
]

实现方案（聚合管道） #

db.collection.aggregate([
  // 展开cars数组，为每个元素生成独立中间文档
  { $unwind: "$cars" },
  // 按原文档ID和parent_company_id分组，收集组内车辆并标记是否含v12车型
  {
    $group: {
      _id: {
        docId: "$_id",
        parentCompanyId: "$cars.parent_company_id"
      },
      name: { $first: "$name" },
      description: { $first: "$description" },
      carsGroup: { $push: "$cars" },
      hasV12: {
        $max: { $in: ["v12", "$cars.model"] }
      }
    }
  },
  // 筛选符合条件的分组：存在指定父公司车辆，且组内有v12车型
  {
    $match: {
      $and: [
        { "carsGroup": { $elemMatch: { parent_company: true, status: "inprogress" } } },
        { hasV12: true }
      ]
    }
  },
  // 调整输出结构，恢复原文档顶层字段
  {
    $project: {
      _id: "$_id.docId",
      name: 1,
      description: 1,
      cars: "$carsGroup"
    }
  }
])

管道阶段说明 #

1. $unwind：将cars数组拆分为单个元素的文档，为后续分组操作提供基础。
2. $group：以原文档ID和parent_company_id作为分组键，聚合同一组的所有车辆数据；同时通过$in判断单辆车是否含v12车型，再用$max确保只要组内有一辆符合就标记hasV12为true。
3. $match：过滤掉不符合要求的分组：必须存在parent_company=true且status=inprogress的车辆，同时组内要有v12车型。
4. $project：重组文档结构，将分组后的车辆数组重命名为cars，并保留原文档的_id、name等字段，与预期结果格式一致。

内容的提问来源于stack exchange，提问作者BlackWooDZZ