Mongodb,find results from array and move to another array

Question

for example：

{
  "groups": [
    ...,
    {
      "id": 1,
      "name": "g1",
      "items": [
        {
          "id": 11,
          "name": "item-11"
        },
        {
          "id": 12,
          "name": "item-12"
        }
      ]
    },
    {
      "_id": 2,
      "name": "g2",
      "items": []
    }
  ]
}

Use 'update', groups[0].items search results, move to groups[1].items.

Expected result:

{
  "groups": [
    {
      "_id": 2,
      "name": "g2",
      "items": [
        {
          "id": 11,
          "name": "item-11"
        },
        {
          "id": 12,
          "name": "item-12"
        }
      ]
    }
  ]
}

Answer 1

Based on answers to this question it looks like the only way to use value of another field in an update is to create a script. You haven't specified what is the expected for groups[0].items so I set it to empty array:

var requests = [];
var cursor = db.getCollection('collection_name').find({});
cursor.forEach(document => { 
    requests.push( { 
        'updateOne': {
            'filter': { '_id': document._id },
            'update': { '$set': { 
                'groups.1.items': document.groups[0].items,
                'groups.0.items': []
                 } 
            }
        }
    });
    if (requests.length === 500) {
        //Execute per 500 operations and re-init
        db.getCollection("collection_name").bulkWrite(requests);
        requests = [];
    }
});

if(requests.length > 0) {
     db.getCollection("collection_name").bulkWrite(requests);
}