Update or Insert object in array in MongoDB

Question

I have the following collection

{
    "_id" : ObjectId("57315ba4846dd82425ca2408"),
    "myarray" : [ 
        {
            userId : "8bc32153-2bea-4dd5-8487-3b65e3aa0869",
            Time:2022-09-20T04:44:46.000+00:00,
            point : 5
        },
        {
            userId : "5020db46-3b99-4c2d-8637-921d6abe8b26",
            Time:2022-09-20T04:44:49.000+00:00
            point : 2
        },        
     ]
}

These are my questions

I want to push into myarray if userId doesn’t exist, and if userid already exists then update time and point also I have to keep only 5 elements in the array if 6th element comes then I a have to sort the array based on Time and remove oldest time entry

what is the best way to do this in mongo using aggregation

FYI we are using Mongo 4.4

Tom Slabbaert · Accepted Answer · 2022-09-21 08:41:51Z

0

You can achieve this by using the aggregation pipeline update syntax, the strategy will be first to update the array (or insert a new element to it).

then if the size exceeds 5 we just filter it based on minimum value. like so:

const userObj = {point: 5, userId: "12345"};

db.collection.updateOne(
{ ...updateCondition },
[
  {
    $set: {
      myarray: {
        $cond: [
          {
            $in: [
              userObj.userId,
              {$ifNull: ["$myarray.userId", []]}
            ]
          },
          {
            $map: {
              input: "$myarray",
              in: {
                $cond: [
                  {
                    $eq: [
                      "$$this.userId",
                      userObj.userId
                    ]
                  },
                  {
                    $mergeObjects: [
                      "$$this",
                      {
                        Time: "$$NOW", // i used "now" time but you can swap this to your input
                        point: userObj.point
                      }
                    ]
                  },
                  "$$this"
                ]
              }
            }
          },
          {
            $concatArrays: [
              { $ifNull: ["$myarray", []] },
              [
                {
                  userId: userObj.userId,
                  point: userObj.point,
                  Time: "$$NOW"
                }
              ]
            ]
          }
        ]
      }
    }
  },
  {
    $set: {
      myarray: {
        $cond: [
          {
            $gt: [
              {
                $size: "$myarray"
              },
              5
            ]
          },
          {
            $filter: {
              input: "$myarray",
              cond: {
                $ne: [
                  "$$this.Time",
                  {
                    $min: "$myarray.Time"
                  }
                ]
              }
            }
          },
          "$myarray"
        ]
      }
    }
  }
])

Mongo Playground

edited Sep 21, 2022 at 8:41

answered Sep 20, 2022 at 7:42

Tom Slabbaert

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6 Comments

Vardhan Over a year ago

getting exception here $myarray.userId when there is no array in document and while inserting for the first time

Tom Slabbaert Over a year ago

You can solve it like this, by initializing the array as an empty [] if it doesn't exist.

Vardhan Over a year ago

Can't we handle that case in pipeline?

Tom Slabbaert Over a year ago

Yes, you mean like this?

Vardhan Over a year ago

mongoplayground.net/p/07YUVMoelcO getting this error when I try it fail to run update: write exception: write errors: [$in requires an array as a second argument, found: missing]

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