how to update a document and merge two array of objects 

Italo_Carrasco_Lucero · 2025-03-25T10:11:59.523Z

Hello everyone, i am using nestjs mongoose, i am trying to update a list concatenating what is currenty in the document with the new given data.

what i have in my code(this is a simplified version) is this:

Query:

      await this.sampleModel.bulkWrite(
        collectors.map((collector) => ({
          updateOne: {
            filter: { master:"111" },
            update: {
              $set: {
                collectorsWithError: {
                  $concatArrays: [
                    '$collectorsWithError',
                    [
                      {
                        collectorId: collector.id,
                      },
                    ],
                  ],
                },
              },
            },
          },
        })),

Document:

{
  "_id": {
    "$oid": "67e1a7979bae1f4ef1c45a7e"
  },
  "master": "111",
  "collectorsWithError": [{}],
  "createdAt": {
    "$date": "2025-03-24T18:42:31.619Z"
  },
  "updatedAt": {
    "$date": "2025-03-24T18:42:31.619Z"
  },
  "__v": 0
}

for some reason the result of this operation is that collectorsWithError becomes an array with an empty object.

if i execute this query in mongo atlas it shows the new array with merged values, so i dont know what i am doing wrong, i tried using $push but it doesnt add the new items to the array.

thanks in advance!

steevej · 2025-03-25T12:04:13.427Z

I am not sure if I understand your update but if I do you would be better serve using

mongodb.com

$push - MongoDB Manual v8.0 - MongoDB Docs

Use the $push operator to append a specified value to an array. $push supports the $each, $slice, $sort, and $position modifiers for advanced array operations.

steevej · 2025-04-04T11:59:07.857Z

@Italo_Carrasco_Lucero, you raised an issue a couple of days ago.

I provided an idea.

I would appreciate a follow up.

Thanks