MongoDB - Update the value of one field with the value of another nested field

Question

I am trying to run a MongoDB query to update the value of one field with the value of another nested field. I have the following document:

{
  "name": "name",
  "address": "address",
  "times": 10,
  "snapshots": [
    {
      "dayTotal": 2,
      "dayHit": 2,
      "dayIndex": 2
    },
    {
      "dayTotal": 3,
      "dayHit": 3,
      "dayIndex": 3
    }
  ]
}

I am trying like this:

db.netGraphMetadataDTO.updateMany( 
    { },
    [{ $set: { times: "$snapshots.$[elem].dayTotal" } }],
    {   
        arrayFilters: [{"elem.dayIndex":{"$eq": 2}}],
        upsert: false,
        multi: true
    }
);

but got an error:

arrayFilters may not be specified for pipeline-syle updates

Answer 1

You can't use arrayFilters with aggregation pipeline for update query at the same time.

Instead, what you need to do:

1. Get the dayTotal field from the result 2.

2. Take the first matched document from the result 3.

3. Filter the document from snapshots array.

db.netGraphMetadataDTO.updateMany({},
[
  {
    $set: {
      times: {
        $getField: {
          field: "dayTotal",
          input: {
            $first: {
              $filter: {
                input: "$snapshots",
                cond: {
                  $eq: [
                    "$$this.dayIndex",
                    2
                  ]
                }
              }
            }
          }
        }
      }
    }
  }
],
{
  upsert: false,
  multi: true
})

Demo @ Mongo Playground