Add an element to an array, if it exists don't add it, if it exists update it

Question

I am making a voting system in which an object will have an array called scores, every time it is qualified a record will be entered to this array as long as the same id does not exist.

Sample Doc :

{
 name:"jose luis",
 scores:[]
}

The user push :

{id:1,stars:5}

Updated Doc :

{
 name:"jose luis",
 scores:[{id:1,stars:5}]
}

The user push 2nd time :

{id:1,stars:4}

Updated Doc :

{
 name:"jose luis",
 scores:[{id:1,stars:4}]
}  //this should update the value of the stars under the array element with the existing id.

I have tried this :

   Politico.update(
        { name: "jose luis" },
        {
            $setOnInsert: { "$scores.id": body.req.id},
            "$addToSet": {
                scores: {
                    "id": body.req.id,
                    "starts": body.req.stars
                }
            }


        },
        { upsert: true }

I have tried this but it doesn't work, how can I fix it? Thanks a lot.

Are you using MongoDB version 4.2 or above ?

whoami - fakeFaceTrueSoul
– whoami - fakeFaceTrueSoul

2020-04-03 23:27:49 +00:00
Commented Apr 3, 2020 at 23:27 — whoami - fakeFaceTrueSoul
– whoami - fakeFaceTrueSoul, Commented Apr 3, 2020 at 23:27
4.2.3 is my current version

yavg
– yavg

2020-04-03 23:54:44 +00:00
Commented Apr 3, 2020 at 23:54 — yavg
– yavg, Commented Apr 3, 2020 at 23:54

whoami - fakeFaceTrueSoul · Accepted Answer · 2020-04-04 00:27:35Z

1

On MongoDB 4.2 or above as you can use aggregation-pipeline in updates, try below query :

Politico.updateOne(
  { name: "jose luis" },
  [{
    $addFields: {
      scores: {
        $reduce: {
          input: "$scores",
          initialValue: [{ id: 1, stars: 5 }], // Input
          in: {
            $cond: [
              { $in: ["$$this.id", "$$value.id"] }, /** Check id exists in 'scores' array */
              "$$value", /** If YES, return input */
              { $concatArrays: ["$$value", ["$$this"]] }/** If NO, concat value(holding array) with current object as array */
            ]
          }
        }
      }
    }
  }]);

You might not need { upsert: true } as you're not writing a new document with name : "jose Luis" & respective scores array. But if you wanted to do that :

Politico.updateOne(
  { name: "jose luis" },
  [{
    $addFields: {
      scores: {
        $reduce: {
          input: "$scores",
          initialValue: [{ id: 1, stars: 5 }], // Input
          in: {
            $cond: [
              { $in: ["$$this.id", "$$value.id"] }, /** Check id exists in 'scores' array */
              "$$value", /** If YES, return input */
              { $concatArrays: ["$$value", ["$$this"]] }/** If NO, concat value(holding array) with current object as array */
            ]
          }
        }
      }
    }
  },
  {$addFields : {scores : { $ifNull: [ "$scores", {id : 13, stars: 3} ] }}} /** This additional 'addFields' will add 'scores' array with input object to newly created doc */
],{upsert : true});

Test : MongoDB-Playground

answered Apr 4, 2020 at 0:27

whoami - fakeFaceTrueSoul

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13 Comments

yavg Over a year ago

Thanks for your valuable help, something strange happens. If I add another item with a different id from the one already found, it doesn't add it, it only updates it. If I enter an element with an id that is not present in the array, I should add it, otherwise update it. I thought the solution would be simpler XD

whoami - fakeFaceTrueSoul Over a year ago

@yavg : Can elaborate you issues, I couldn't understand what's happening, Please provide some examples..

whoami - fakeFaceTrueSoul Over a year ago

@yavg : That playground only for finds/aggregation, You need to test it in DB with update() !! It should work as expected..

yavg Over a year ago

excuse my ignorance, there are things that are not clear to me. for example, when you use the $ symbol twice, and what is the $reduce for in this case? you are the best!

yavg Over a year ago

Thank you very much, I am sorry to ask you again for help and bother you.

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