Setting the field of an arrayFilter match to the value of another field

Question

Note: This is not related to questions asking for how to update a field value to another field's value, because those do not include array filter matches.

I have the following query:

db.UserNotifications.updateOne(
    {_id:ObjectId("5c5c39e94c9d4404d4577e94")}, 
    {$set:{
        "Notifications.$[match].Group.ActualUnreadCount": 50,
        "Notifications.$[match].Group.UnreadCountSnapshot": "Notifications.$[match].Group.ActualUnreadCount"
    }},
    {arrayFilters:[{
        "match.Group.Id": "some-id"
    }]});

Now, what I wanted to do with this is set the value of UnreadCountSnapshot for the match in the array, to the value of the ActualUnreadCount of the same match.

Instead, UnreadCountSnapshot just gets set to the string "Notifications.$[match].Group.ActualUnreadCount".

Any ideas on how to implement this?

Here's a sample document in the collection:

{
    "_id": {
        "$oid": "5c5c39e94c9d4404d4577e94"
    },
    "Notifications": [{
        "Object": {
            "_id": "5e3967cc9fc5720001d7100f",
            "Type": "Transaction"
        },
        "Change": {
            "Verb": "Create",
            "TimeUtc": {
                "$date": "2020-02-04T12:47:08.796Z"
            },
            "Actors": []
        },
        "Group": {
            "TotalCount": 2,
            "ActualUnreadCount": 50,
            "UnreadCountSnapshot": 23,
            "ReadTimeUtc": {
                "$date": "2020-08-26T10:24:32.602Z"
            },
            "ViewTimeUtc": {
                "$date": "2020-08-26T10:24:32.602Z"
            }
        }
    }],
    "LastNotificationTimeUtc": {
        "$date": "2019-02-21T10:18:57.456Z"
    },
    "LastDeletedNotificationTimeUtc": {
        "$date": "2020-08-26T10:24:30.374Z"
    }
}

turivishal · Accepted Answer · 2020-08-26T14:25:16.340

The arrayFields can not allow to assign any reference field value to another field, You can use update document with aggregation pipeline from MongoDB v4.2,

db.UserNotifications.updateOne(
  { _id: ObjectId("5c5c39e94c9d4404d4577e94") },
  [{
    $set: {
      Notifications: {
        $map: {
          input: "$Notifications",
          in: {
            $mergeObjects: [
              "$$this",
              {
                $cond: [{
                    $eq: [
                      "$$this.Object._id",
                      "5e3967cc9fc5720001d7100f" // some id
                    ]
                  },
                  {
                    Group: {
                      $mergeObjects: [
                        "$$this.Group",
                        {
                          ActualUnreadCount: 50, // add update number
                          UnreadCountSnapshot: "$$this.Group.ActualUnreadCount"
                        }
                      ]
                    }
                  },
                  {}
                ]
              }
            ]
          }
        }
      }
    }
  }]
)

Playground

Setting the field of an arrayFilter match to the value of another field

1 Answers1