Node Driver - How to updateMany Replace Array with last item in Array

Working with Data Drivers
, ,
1

I have a document with a Array called ‘lastLogin’ which has all the recent timestamps.

I would like to overwrite this array with a single element being the last index value in the array.

from
{
lastLogin : [timestamp1,timestamp2,timestamp3]
}

to

{
lastLogin : timestamp3
loginTimes : 3
}

So overwrite the lastLogin array with a single value of the last index
Add a field called loginTimes which is the total count of the lastLogin Array. (edited)

Not sure exactly how to do this either using aggregation or normal commands.

Tks.

2

Hi @Rishi_uttam,

I made this aggregation pipeline and I think it gets the job done.

[
  {
    '$unwind': {
      'path': '$lastLogin'
    }
  }, {
    '$group': {
      '_id': '$_id', 
      'lastLogin': {
        '$last': '$lastLogin'
      }, 
      'loginTimes': {
        '$sum': 1
      }
    }
  }, {
    '$merge': {
      'into': 'coll', 
      'on': '_id', 
      'whenMatched': 'merge', 
      'whenNotMatched': 'fail'
    }
  }
]

Test it before running in prod because it overwrites the lastLogin field as you requested. But you could also write the $last value into another field just to be safe if you prefer.

Cheers,
Maxime.

1 Like
3

wow thank you, thats great… i will test it out…

would the same be possible without using aggregation and mongo query language? i…e updateMany with $set?

4

Humm maybe but I’m not sure. At least this is its equivalent and I don’t know if the version without the aggregation pipeline is possible. At least I have no idea how I would do it if it’s even possible. Why is this important?

5

Ahh you mean using normal query language without aggregation may not be possible in one single operation?

i would like to learn actually how to do it without aggregation as im not to familiar with aggregation at this point, but thanks so much.

Rishi

6

Then this course was especially designed for you! And it’s free :tada: !

I don’t even know how to reuse the value of an existing field in the document without the aggregation framework. Maybe there is a way but the aggregation framework is really like super powers!

Using MongoDB without the aggregation framework is like using a motorbike without putting gas in it. :smiley: ! You will eventually be able to get to your destination but this is going to require a lot more effort and it won’t be efficient :slight_smile:.

I did some research before sending this answer and there is a way to do this with an “update” operation. But you will also need the aggregation pipeline which can now be used in the update operations… :muscle:. So it’s aggregation or aggregation basically.

Cheers,
Maxime.

2 Likes
7

Hi, Thanks I already started the course, and hope to learn a lot from it.

I did not know that agg framework can also update, insert data, i thought it was for reading data only.

1 Like
8

You have the list of all the stages here.

$out and $merge can write data into a collection. :slight_smile: