How to retrieve last update time of each document in MongoDB?

Question

I would like to know if there is a way to get the last update/modify time of data (i.e documents) in a collection in MongoDB. More clearly, I want to make a query to retrieve al

Answer 1

You can do the following. With MongoDB version 4.2+, you can now perform aggregation operators like $toDate to extract the timestamp from ObjectId "_id" and update at the same time.

Here we use the aggregate query $toDate to extract the timestamp from MongoDB's ObjectId "_id" field and update the documents using {$replaceRoot: {newRoot: "$$ROOT"}} instead of explicitly stating $set

var collection = "person"

agg_query = [
    {
        "$addFields" : {
            "_last_updated" : {
                "$toDate" : "$_id"
            }
        }
    },
    {
        $replaceRoot: {
            newRoot: "$$ROOT"
        } 
    }
]

db.getCollection(collection).updateMany({}, agg_query, {upsert: true})