在 Mongodb 中查找和聚合多级子文档

Question

我已经使用 $lookup、$unwind 和 $match 尝试了很多类似问题的答案，但我无法让这个解决我的 sub-sub-subdocument 情况。

我有这个collection，东西：

{
    "_id" : ObjectId("5a7241f7912cfc256468cb27"),
    "name" : "Fortress of Solitude",
    "alias" : "fortress_of_solitude",
},
{
    "_id" : ObjectId("5a7247ec548c9ad042f579e2"),
    "name" : "Batcave",
    "alias" : "batcave",
},
{
    "_id" : ObjectId("6a7247bc548c9ad042f579e8"),
    "name" : "Oz",
    "alias" : "oz",
},

和这个one-documentcollection，地点：

{
    "_id" : ObjectId("5b9acabbbf71f39223f8de6e"),
    "name" : "The Office",
    "floors" : [ 
        {
            "name" : "1st Floor",
            "places" : [ 
                {
                    "name" : "Front Entrance",
                    "alias" : "front_entrance"
                }
            ] 
        }, 
        {
            "name" : "2nd Floor",
            "places" : [ 
                {
                    "name" : "Batcave",
                    "alias" : "batcave"
                },
                {
                    "name" : "Oz",
                    "alias" : "oz"
                }
           ]
        }
    ]
}

我想要 return 所有事物，但是如果事物和地点之间的别名匹配，则场所的 floors.places.name 与每个事物聚合（如果存在）。所以，我想 return:

{
    "_id" : ObjectId("5a7241f7912cfc256468cb27"),
    "name" : "Fortress of Solitude",
    "alias" : "fortress_of_solitude",
                                 <-- nothing added here because
                                 <-- it's not found in Venues
},
{
    "_id" : ObjectId("5a7247ec548c9ad042f579e2"),
    "name" : "Batcave",
    "alias" : "batcave",
    "floors" : [                        <-- this should be 
        {                               <-- returned 
            "places" : [                <-- because 
                {                       <-- the alias
                    name" : "Batcave"   <-- matches
                }                       <-- in Venues
            ]                           <-- 
        }                               <-- 
    ]                                   <--     
},
{
    "_id" : ObjectId("6a7247bc548c9ad042f579e8"),
    "name" : "Oz",
    "alias" : "oz",
    "floors" : [                        <-- this should be 
        {                               <-- returned 
            "places" : [                <-- because 
                {                       <-- the alias
                    name" : "Oz"        <-- matches
                }                       <-- in Venues
            ]                           <-- 
        }                               <-- 
    ]                                   <--     
}

我已经得到了以下查询，但它只是 return 将整个 Venues.floors 数组作为每个事物的聚合，这是聚合了太多无关数据的方式。我只想将 Venues 中的每个相关 floor.place sub-subsubdocument 合并到其对应的 Thing 中（如果它存在于 Venues 中）。

db.getCollection('things').aggregate([
  {$lookup: {from: "venues",localField: "alias",foreignField: "floors.places.alias",as: "matches"}},
  {
    $replaceRoot: { newRoot: { $mergeObjects: [ { $arrayElemAt: [ "$matches", 0 ] }, "$$ROOT" ] } }
  },
  { $project: { matches: 0 } }  
])

我正在努力解决现有的答案，这些答案似乎在 MongoDB 版本 3.2、3.4、3.6 或 4.2 中发生了变化，包括或不包括 $unwind、$pipeline 和其他术语。有人可以解释如何像这样聚合 sub-sub-subdocument 吗？谢谢！

Answer 1

从 MongoDB v3.6 开始，我们可以执行 uncorrelated sub-queries 这让我们更灵活地加入两个集合。

试试这个：

db.things.aggregate([
  {
    $lookup: {
      from: "venues",
      let: {
        "alias": "$alias"
      },
      pipeline: [
        {
          $unwind: "$floors"
        },
        {
          $project: {
            _id: 0,
            places: {
              $filter: {
                input: "$floors.places",
                cond: {
                  $eq: [
                    "$$alias",
                    "$$this.alias"
                  ]
                }
              }
            }
          }
        },
        {
          $match: {
            "places.0": {
              $exists: true
            }
          }
        },
        {
          $unset: "places.name"
        }
      ],
      as: "floors"
    }
  }
])

MongoPlayground

Answer 2

你可以试试这个：

db.things.aggregate([
    {
        $lookup:
        {
            from: "venues",
            let: { alias: "$alias" },
            pipeline: [
                { $unwind: { path: "$floors", preserveNullAndEmptyArrays: true } },
                { $match: { $expr: { $in: ['$$alias', '$floors.places.alias'] } } },
                /**  Below stages are only if you've docs like doc 2 in Venues */
                { $addFields: { 'floors.places': { $filter: { input: '$floors.places', cond: { $eq: ['$$this.alias', '$$alias'] } } } } },
                { $group: { _id: '$_id', name: { $first: '$name' }, floors: { $push: '$floors' } } },
                {$project : {'floors.places.alias': 1, _id :0}} // Optional
            ],
            as: "matches"
        }
    }
])

测试： MongoDB-Playground

在 Mongodb 中查找和聚合多级子文档

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