How to check if an array has the same elements as another one in mongodb aggregation

Question

I need to match all documents where field arr, which is an array of object Ids, has same elements of a given one no matther the position.

I tried:

[
  {
    $match:{
      arr: givenArr
    }
  }
]

or

[
  {
    $match:{
      arr: {
          $in: givenArr
        }
    }
  }
]

The first pipeline matches all the documents that have same elements in the same position.

The second pipeline matches all the documents that has at least one element in the given array.

For example if I have a couple of documents like:

[
  {
    _id: ObjectId("639a0e4cc0f6595d90a84de4"),
    arr: [
      ObjectId("639a0e4cc0f6595d90a84de1"),
      ObjectId("639a0e4cc0f6595d90a84de2"),
      ObjectId("639a0e4cc0f6595d90a84de3"),
    ]
  },
  {
    _id: ObjectId("639a0e4cc0f6595d90a84de5"),
    arr: [
      ObjectId("639a0e4cc0f6595d90a84de7"),
      ObjectId("639a0e4cc0f6595d90a84de8"),
      ObjectId("639a0e4cc0f6595d90a84de9"),
    ]
  },
]

If I need to match all of those documents that have arr same as

[
  ObjectId("639a0e4cc0f6595d90a84de8"),
  ObjectId("639a0e4cc0f6595d90a84de9"),
  ObjectId("639a0e4cc0f6595d90a84de7"),
]

I want to get only the second document.

How could I do that?

rickhg12hs · Accepted Answer · 2023-01-29 16:08:49Z

3

You could treat each array as a set and use "$setEquals".

db.collection.find({
  $expr: {
    $setEquals: [
      "$arr",
      [
        ObjectId("639a0e4cc0f6595d90a84de8"),
        ObjectId("639a0e4cc0f6595d90a84de9"),
        ObjectId("639a0e4cc0f6595d90a84de7")
      ]
    ]
  }
})

Try it on mongoplayground.net.

answered Jan 29, 2023 at 16:08

rickhg12hs

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1 Comment

Loudrous Over a year ago

For those who needs $setEquals works also in $project pipeline with aggregation framework. GG @rickhg12hs

ray · Accepted Answer · 2023-01-29 15:11:17Z

2

You can compare the sorted results of your 2 arrays computed by $sortArray

db.collection.find({
  $expr: {
    $eq: [
      {
        $sortArray: {
          input: "$arr",
          sortBy: 1
        }
      },
      {
        $sortArray: {
          input: [
            ObjectId("639a0e4cc0f6595d90a84de8"),
            ObjectId("639a0e4cc0f6595d90a84de9"),
            ObjectId("639a0e4cc0f6595d90a84de7"),
            
          ],
          sortBy: 1
        }
      }
    ]
  }
})

Mongo Playground

answered Jan 29, 2023 at 15:11

ray

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