如何在同一集合中使用循环查询 mongodb，直到我找到 null 或空值？

Question

I have stacked in a nested object. here is my collection.

{
"key": 1,
"subKey": ""
},
{
"key": 2,
"subKey": 1
},
{
"key": 3,
"subKey": 2
},
{
 "key": 4,
 "subKey": 3
}

I want to query Key:4 , which gives me result

{
 "key": 4,
 "subKey": 3
}

after getting result i want to query "subKey": 3 as a key:"$subKey" and i want to run a loop, until i find a empty subKey in our case It is Key:1 . and whenever i found an empty subKey i want it document as a parent.

In the end, I want the result

{
 "key": 4,
 "parent":{"key":1,"subKey":"",....}
}

or similar.

Is it possible by using MongoDB built-in function? if not available how do I achieve this goal?

also, I want an alternative solution for it if there is.

Answer 1

You can achieve using $graphLookup

play

db.collection.aggregate([
  {
    $graphLookup: {
      from: "collection",
      startWith: "$key", 
      connectFromField: "subKey",
      connectToField: "key",
      as: "keys"
    }
  }
])

If you want a match filter add it,

play

db.collection.aggregate([
  {
    $match: {
      key: 4
    }
  },
  {
    $graphLookup: {
      from: "collection",
      startWith: "$key",
      connectFromField: "subKey",
      connectToField: "key",
      as: "keys"
    }
  }
])

Important consideration:

The $graphLookup stage must stay within the 100 MiB memory limit. If allowDiskUse: true is specified for the aggregate() operation, the $graphLookup stage ignores the option

To transform the data, you cannot have duplicate keys in parent object. So parent should be an array

play

db.collection.aggregate([
  {
    $match: {
      key: 4
    }
  },
  {
    $graphLookup: {
      from: "collection",
      startWith: "$key",
      connectFromField: "subKey",
      connectToField: "key",
      as: "keys"
    }
  },
  {
    "$addFields": {
      "parent": {
        "$map": {
          "input": "$keys",
          "as": "res",
          "in": {
            "key": "$$res.key",
            "subKey": "$$res.subKey"
          }
        }
      },
      "key": "$key",
      
    }
  },
  {
    $project: {
      keys: 0
    }
  }
])