MongoDB count fields with condition

Question

in my collection i have an document that contains following array (simplyfied):

 notifications: [
    {
       message: "i am an message",
       readed: false
    },
    {
       message: "i am an message",
       readed: false
    },
    {
       message: "i am an message",
       readed: true
    },
    {
       message: "i am an message",
       readed: true
    }
 ]

I want to count all fields with readed:false so that is my expected result:

{
   unreaded_messages: 2
}

I have tried to add an field and to map over the notification array and to add all unreaded elements. after that i wanted to get the size with $size so i get an number. But it doesnt worked how i expected.

{
$addFields: {
  unreaded_messages: {
    $map: {
      input: "$notification",
      in: {
        check: {
          $eq: [
            "$$this.readed",
            false
          ]
        }
      }
    }
  }
}
}

Ashh · Accepted Answer · 2020-04-17 08:43:21Z

1

You can use below aggregation

{
  "$addFields": {
    "unreaded_messages": {
      "$size": {
        "$filter": {
          "input": "$notification",
          "cond": {
            "$eq": ["$$this.readed", false]
          }
        }
      }
    }
  }
}

answered Apr 17, 2020 at 8:43

Ashh

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