嵌套localfield时的$lookup

MongoDB版本3.4.10 (应用程序正在使用Meteor框架)

目标 :根据运行时的需要,将ID引用的文档聚合到包含文档中。

我有 Materials ,请 Models ,和 Catalog 包含以下文档的集合:

材料

 { "_id" : "cf4KgXw7ZK6ukdzR7", "name" : "parquet_wood_mahogany" }

模型

{
  "_id" : "Mwp5eYYZ4GZzvZuoK",
  "name" : "top_square_chamfered",
  "type" : "top"
}
{
  "_id" : "CqhS2m2RcLZ2Bm4eb",
  "name" : "skirt_square",
  "type" : "skirt"
}
{
  "_id" : "dYP22ajALnWBwpBj2",
  "name" : "leg_square",
  "type" : "leg"
}

目录

{
  "_id" : "EcRGzPAq79giYKrbY",
  ...,
  "specs" : {
    ...,
    "models" : [
      {
        "mesh" : "Mwp5eYYZ4GZzvZuoK",
        "material" : "cf4KgXw7ZK6ukdzR7"
      },
      {
        "mesh" : "CqhS2m2RcLZ2Bm4eb",
        "material" : "cf4KgXw7ZK6ukdzR7"
      },
      {
        "mesh" : "dYP22ajALnWBwpBj2",
        "material" : "cf4KgXw7ZK6ukdzR7"
      }
    ]
  }
}

渴望的 聚合后返回的文档格式:

{
  "_id" : "EcRGzPAq79giYKrbY",
  ...,
  "specs" : {
    "dimensions" : {
      ...,
    },
    "models" : [
      {
        "mesh" : {
          "_id" : "Mwp5eYYZ4GZzvZuoK",
          "name" : "top_square_chamfered",
          "type" : "top"
        },
        "material" : {
          "_id" : "cf4KgXw7ZK6ukdzR7",
          "name" : "parquet_wood_mahogany"
        }
      },
      {
        "mesh" : {
          "_id" : "CqhS2m2RcLZ2Bm4eb",
          "name" : "skirt_square",
          "type" : "skirt"
        },
        "material" : {
          "_id" : "cf4KgXw7ZK6ukdzR7",
          "name" : "parquet_wood_mahogany"
        }
      },
      {
        "mesh" : {
          "_id" : "dYP22ajALnWBwpBj2",
          "name" : "leg_square",
          "type" : "leg"
        },
        "material" : {
          "_id" : "cf4KgXw7ZK6ukdzR7",
          "name" : "parquet_wood_mahogany"
        }
      }
    ]
  }
}

我没有包括我的任何查询代码,因为它是如此远离标记,只是噪音。我一直想用 aggregate ,与 $lookup 组合,但我不会接近我想要的。MongoDB 3.6版 pipeline 语法将使这更容易…但我在v3.4中完全不知所措。

如果可能的话,我希望避免使用多个数据库请求来组合这些信息。如能提供任何建议,我们将不胜感激!

编辑:工作解决方案-

db.catalog.aggregate([
  { "$lookup": {
    "from": 'models',
    "localField": "specs.models.mesh",
    "foreignField": "_id",
    "as": "models.mesh"
  }},
  { "$lookup": {
    "from": 'materials',
    "localField": "specs.models.material",
    "foreignField": "_id",
    "as": "models.material"
  }},
  { "$unwind": "$models.mesh" },
  { "$unwind": "$models.material" },
  { "$group":{
    "_id": "$_id",
    "title": { "$first": "$title" },
    "desc": { "$first": "$desc" },
    "thumbnail": { "$first": "$thumbnail" },
    "createdBy": { "$first": "$createdBy" },
    "createdAt": { "$first": "$createdAt" },
    "specs": { "$first": "$specs" },
    "models": { "$push": "$models" }
  }},
  { "$project": {
    "_id": "$_id",
    "title": "$title",
    "desc": "$desc",
    "thumbnail": "$thumbnail",
    "createdBy": "$createdBy",
    "createdAt": "$createdAt",
    "specs.dimensions": "$specs.dimensions",
    "specs.models": "$models",
  }}
])