Mongodb how to find docs with more than 2 array items with specific value

Question

can somebody tell me please how to find items in Mongodb array which contains more than 2 items with specific value? For example if I have two documents like this:

{
    someArray: [
        {'aaa' => 1},
        {'aaa' => 1}
    ]
}
{
    someArray: [
        {'aaa' => 1},
        {'aaa' => 2}
    ]
}

I need to find the first document which contains two items which 'aaa' value is 1. I dont mean $elemMatch I need to count the number of the matched items. Thanks for any help.

I dont understand. Output should be the document. For my purpose _id will be enough. — Čamo
– Čamo, Commented May 24, 2019 at 17:14

mickl · Accepted Answer · 2019-05-24 17:15:02Z

1

You can use below aggregation:

db.col.aggregate([
    {
        $match: {
            $expr: {
                $gte: [
                    { $size: { $filter: { input: "$someArray", cond: { $eq: [ "$$this.aaa", 1 ] } } } },
                    2
                ]
            }
        }
    },
    {
        $limit: 1
    }
])

$filter allows you to apply your condition, then you can use $size to get the length of filtered array and compare it againts your value using $gte

answered May 24, 2019 at 17:15

mickl

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Comments

Ashh · Accepted Answer · 2019-05-24 17:32:25Z

0

You can use $indexOfArray to find whether the array contains that element and then compare with the $size of the array using $eq

db.collection.find({
  "$expr": {
    "$and": [
      { "$ne": [{ "$indexOfArray": ["$someArray.aaa", 1] }, -1] },
      { "$eq": [{ "$size": "$someArray" }, 2] }
    ]
  }
}).limit(1)

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answered May 24, 2019 at 17:32

Ashh

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2 Comments

mickl Over a year ago

It's all about interpretation here, and what actually means "two items which 'aaa' value is 1", in this case any of them has to have aaa set to 1, I'm not sure if that's the point

Ashh Over a year ago

:-):-):-) Yes. Even I am confused now. I thought may be any of the element contains value 1. But I think you are right both elements should contain the 1. Let's see what OP needs. Most probably you are right.

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