MongoDB 聚合，使用一个文档中的值作为另一个文档中的键

Question

因此，我尝试聚合两个在 id 上匹配并基于第一个文档的值的文档。

文档 1

{
“id”:3
“Whats for dinner”: “dinner”,
“What is for dinner tonight”: “dinner”,
“Whats for lunch”:“lunch”
}

文件 2

{
“Id”:3
“dinner” : “We are having roast!”,
“lunch” : “We are having sandwiches”
}

我想从匹配 id 开始，测试 doc1 中是否存在问题。然后 return 来自 doc1 的问题和来自 doc 2 的答案。喜欢

{“Whats for dinner”:“We are having roast!”}

我试过：

{ “$match”: { “id”: 3, “Whats for dinner”:{"$exists":True}} },

{
    "$lookup": {
        "from": "doc 2", 
        "localField": "id", 
        "foreignField": "id", 
        "as": "qa"
    }
}

但是从这里我无法弄清楚如何将 doc1 中的值用作 doc2 中的键

可能很简单！但我是新手，就是无法让它工作！？

Answer 1

疯狂的数据模型！这将是一个解决方案：

db.doc1.aggregate([
  { $project: { data: { $objectToArray: "$$ROOT" } } },
  { $unwind: "$data" },
  {
    $lookup: {
      from: "doc2",
      pipeline: [
        { $project: { data: { $objectToArray: "$$ROOT" } } }      
      ],
      as: "answers"
    }
  },
  {
    $set: {
      answers: {
        $first: {
          $filter: {
            input: { $first: "$answers.data" },
            cond: { $eq: [ "$$this.k", "$data.v" ] }
          }
        }
      }
    }
  },
  { $match: { answers: { $exists: true } } },
  {
    $project: {
      data: [
        {
          k: "$data.k",
          v: "$answers.v"
        }
      ]
    }
  },
  { $replaceWith: { $arrayToObject: "$data" } }
])

Mongo Playground

最好不要使用任何用户数据作为键名，您将始终需要兼顾 $objectToArray 和 $arrayToObject

也许可以考虑一下：

questions: { 
   guildid: 3, 
   text: [
      "Whats for dinner",
      "What is for dinner tonight",
      "Whats for lunch"
   ], 
   "nospace": 1
}

MongoDB 聚合，使用一个文档中的值作为另一个文档中的键

MongoDB aggregation, use value from one document as key in another

lookup

key

aggregation

mongodb