MongoDB - get subdocuments from arbitrary depth and object structure-CodePudding

I have a collection that has objects of various random structures/depths. Within them, there is one object that I want to get as my results, which has a specific key/value pair that I can use to find them.

An example from my collection:

{
    "_id": ObjectId("123"),
    "someKey": "blue",
    "children": [
        {
            "foo": "bar",
            "anotherKey": "anotherValue",
            "whateverA": 111
        }
    ]
}
{
    "_id": ObjectId("456"),
    "blahKey": "dog",
    "children": [
        {
            "anotherRandom": "randomValue",
            "children": [
                {
                    "moreRandom": "stuffValue",
                    "children": [
                        {
                            "foo": "bar",
                            "animalKey": "legsValue",
                            "whateverB": 222
                        }
                    ]
                }
            ]
        }
    ]
}

I would like to search for subdocuments that contain "foo: bar", and get a result that looks like the following:

{
    "foo": "bar",
    "anotherKey": "anotherValue",
    "whateverA": 111
}
{
    "foo": "bar",
    "animalKey": "legsValue",
    "whateverB": 222
}

Then I can paginate the results. Is this even possible in MongoDB 5?

Thank you.

CodePudding user response：

If we use the solution of @rickhg12hs

You can do something like:

db.collection.aggregate([
  {
    $addFields: {
      res: {
        $function: {
                 body: "function drill(t, n) {if (n.length > 0){for (let elem of n){if(elem['foo'] && elem['foo'] === 'bar'){t.push(elem);}else {drill(t, elem.children)}}}return t}",
          args: [
            [],
            "$children"
          ],
          lang: "js"
        }
      }
    }
  },
  {
    $project: {
      res: {$arrayElemAt: ["$res", 0]},
      _id: 0
    }
  },
  {
    $replaceRoot: {newRoot: "$res"}
  }
])

As you can see on this playground example.

We can use $function to recursively look for this key named foo and return the object that contains it.

Edit according to a question in the comment:

You can use your code to manipulate it according to your needs: for example in js:

const key = 'foo';
const val = 'bar';
const body = `function drill(t, n) {if (n.length > 0){for (let elem of n){if(elem[${key}] && elem[${key}] === ${val}){t.push(elem);}else {drill(t, elem.children)}}}return t}`;


db.collection.aggregate([
  {
    $addFields: {res: {$function: {body, args: [[], "$children"], lang: "js"}}}
  },
  {
    $project: {
      res: {$arrayElemAt: ["$res", 0]}, _id: 0}
  },
  {
    $replaceRoot: {newRoot: "$res"}
  }
])