mongodb: how to make selection

Question

I Have a mongodb with objects like this:

{
    "_id" : "7XXXXXXXXXX",
    "apps" : [ 
        {
            "id" : "e0d538e0df9a345e",
            "os" : "android",
            "token" : "f1zp-VSi7Ec:APA91bEAbfH8nMeVidkIjPrJ28WHRFDy-BhvKCQdDSdCYsylUzET9GjbPHjofCrr1NMQurinMCI4fuiF7VWNPXne-80op_h0MloK217kc1zKptdo9FTgAH5R932uDphcyB1xQ27-AFdR",
            "version" : "3.2.1",
            "build" : "8115680e",
            "timestamp" : NumberLong(1571740696818)
        }
    ]
}

How i can select objects older certain date using timestampin my case, for example older 3 month?

Possible duplicate of [MongoDB query for document older than 30 seconds](https://stackoverflow.com/questions/21591125/mongodb-query-for-document-older-than-30-seconds) — Matheus Hatje, Oct 22 '19 at 11:01

niranjan_harpale · Answer 1 · 2019-10-22T14:02:52.253

0

You can use $toDate operator in aggregation to do the desired operation,

I hope you are using mongo version 4.0+

$toDate is supported in mongo version 4.0 and on

let selectedDate = new Date();
selectedDate.setDate(d.getDate()-30); //subtracting 30 days from today's date

db.collection("your_collection_name").aggregate({$unwind:{ path: "$apps"}},
    {$addFields: { dateValue: {$toDate: "$apps.timestamp" }}}, 
    {$match: { dateValue: {$lte: selectedDate }}},
    (err, result) => {
       //perform your desired operations
    });

Explanation:

basically, I am first unwinding apps array, which will result in having a separate document of each entry in apps.

Then operate on the timestamp field in each document, and convert it into a proper date with $toDate.

Then in the next stage apply your filter with $match.

UPDATE (from comments):

as you are using mongo version 3.2 the above solution will not work.

then I think, you can opt for another approach here:

Query all your documents in this particular collection, find the proper date from the timestamp field.
Update each document with a new field which will now have the value of computed date from the above step, and save it.
I suggest you write a migration script for the above two steps.
Make sure when inserting a new document, you already add this newly computed date field.

Then you can have simple query like:

db.collection("your_collection_name").find({"app.newDateField": {$lte: {selectedDate }}}, 
    { "apps.$": 1}, 
    (err, result)=>{

    })

edited Oct 22 '19 at 14:02

answered Oct 22 '19 at 12:59

niranjan_harpale

2,048
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Failed to execute script. I use mongo 3.2.0 and i got this error when i try run this script: Error: TypeError: redeclaration of let selectedDate Details: @(shell):1:5 – Valentines Owl Oct 22 '19 at 13:26
whether there is a way do this on mongo 3.2.0? – Valentines Owl Oct 22 '19 at 13:31
unfortunately, this is production database, and i can not change or add any fields – Valentines Owl Oct 22 '19 at 14:28
You have a few options here... **1.** you add a new field from the timestamp and use that for your calculations. – niranjan_harpale Oct 23 '19 at 06:05
**2.** you update each document and change `timestamp` only to contain a date in ISO format. Then have a simple query as shown in above ans. – niranjan_harpale Oct 23 '19 at 06:06
**3.** You just take out all docs and then convert timestamp to date after the query is run, then filter out the result. – niranjan_harpale Oct 23 '19 at 06:08

mongodb: how to make selection

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