mongodb: how to make selection - mongodb

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?

Answer 1

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)=>{
})