How to use find for nested object of objects in MongoDB

Question

I have nested object of objects. Each document in collection looks like this:

{
   anything: "whatever",
   something: {
      // find inside of these document
      a: { getThis: "wow" },
      b: { getThis: "just wow" },
      c: { getThis: "another wow" }
   }
}

I would like to find in every getThis from each document in something.

For example I would like to find document which has getThis: "wow".

I've tried to use something like wildcard with *:

{"something.*.getThis": "wow" }

I've also tried $elemMatch but it seems it works only with array;

{ something: { $elemMatch: { getThis: "wow" } } }

turivishal · Accepted Answer · 2020-09-03 16:01:01Z

1

You can try using $objectToArray,

$addFields to convert something to array in somethingArr
$match condition getThis is wow or not
$project to remove somethingArr

db.collection.aggregate([
  {
    $addFields: {
      somethingArr: { $objectToArray: "$something" }
    }
  },
  { $match: { "somethingArr.v.getThis": "wow" } },
  { $project: { somethingArr: 0 } }
])

Playground

Second possible way

$filter input something as array, convert using $objectToArray
filter will check condition getThis is equal to wow or not

db.collection.aggregate([
  {
    $match: {
      $expr: {
        $ne: [
          [],
          {
            $filter: {
              input: { $objectToArray: "$something" },
              cond: { $eq: ["$$this.v.getThis", "wow"] }
            }
          }
        ]
      }
    }
  }
])

Playground

edited Sep 3, 2020 at 16:01

answered Sep 3, 2020 at 15:55

turivishal

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