Set new field to true/false if an array contains a specific value or not

Question

If $myDogsName is in the array dogNamesOfWinnersArray then myDogWins should be true if its not in the array it should be false.

Is this even possible?

    db.collection.aggregate([
        {
            $addFields: { myDogWins: { $myDogsName: [ "$dogNamesOfWinnersArray", [] ] } }
        }
    ])

the array looks like

dogNamesOfWinnersArray: [
        {
            "name" : "jake", 
            "age" : 6, 
            "breed" : "Bulldog", 
            ...
        },
        {
            "name" : "fred", 
            "age" : 8, 
            "breed" : "Bulldog",
            ... 
        },

    ]

$myDogsName is jake so I expect myDogWins to be true

Sede · Accepted Answer · 2019-12-21 12:32:54Z

3

The $in operator is what you need.

{
  "$addFields": {
    "myDogWins": {
      "$in": [
        "$myDogsName",
        "$dogNamesOfWinnersArray.name"
      ]
    }
  }
}

edited Dec 21, 2019 at 12:32

answered Dec 21, 2019 at 11:51

Sede

61.5k20 gold badges158 silver badges162 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Bill Over a year ago

$myDogsName is just a string, $dogNamesOfWinnersArray is an array and the name can be found at $dogNamesOfWinnersArray.name

Sede Over a year ago

If I understand, the array elements are subdocuments. Is that correct?

Bill Over a year ago

I updated my question for clarity, how do I add name on the end of dogNamesOfWinnersArray

Bill Over a year ago

I've tried to run it but I get no data back at all, I feel that $dogNamesOfWinnersArray.name needs to be somthing like $dogNamesOfWinnersArray[x].name where x is the iterator?

Sede Over a year ago

No indexing. demo

prasad_ · Accepted Answer · 2019-12-21 12:45:07Z

0

db.dogs.save( { _id: 1, name: "jake" } )
db.dogs.save( { _id: 2, name: "jake2" } )

db.dogs.aggregate( [
  { 
      $addFields: { 
          dogNamesOfWinnersArray: { 
              $concatArrays: [ [ ], dogNamesOfWinnersArray ] 
          } 
      } 
  },
  { 
      $addFields: { 
          myDogWins: { $in: [ "$name", "$dogNamesOfWinnersArray.name" ] } 
      } 
  },
  { 
      $project: { dogNamesOfWinnersArray: 0 } 
  }
] )

The output:

{ "_id" : 1, "name" : "jake", "myDogWins" : true }
{ "_id" : 2, "name" : "jake2", "myDogWins" : false }

answered Dec 21, 2019 at 12:45

prasad_

14.4k2 gold badges27 silver badges44 bronze badges

Collectives™ on Stack Overflow

Set new field to true/false if an array contains a specific value or not

2 Answers 2

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related