how to convert timestamp to date in mongodb?

Question

i am working on aggregation of mongodb collection.my mongodb collection has creation_time in timestamp.How will i can collect same day result and aggregate with next day result.Suppose i have to collect data for 5 days.My mongodb collection is:

{
    "_id" : "1522845653126"
},
{
    "_id" : "1522838153324"
},
{
    "_id" : "1513421466415"
},
{
    "_id" : "1515488183153"
},
{
    "_id" : "1521571234500"
}

How can i calculate.How many entry are save on specific date?? nd suppose I want is to query results that returns a running total of the aggregation, like:

{
 time: "2013-10-10"
 count: 3,

},
{
 time: "2013-10-11"
 total: 7,

}

something like this. i have tried to do something like this

db.coll.aggregate([
   {
        $group:{
        _id:new Date($creation_time).toLocaleDateString(),
         $count:{$add:1}
            }
         time:new Date($creation_time).toLocaleDateString()
   }
 ])

It does not work.where am i doing wrong??I am new to mongodb. Thanks for any help

Answer 1

You can use $toDate aggregation to convert timestamp to ISO date and $toLong to convert string timestamp to integer value in mongodb 3.6

db.collection.aggregate([
  { "$project": {
    "_id": {
      "$toDate": {
        "$toLong": "$_id"
      }
    }
  }},
  { "$group": {
    "_id": { "$dateToString": { "format": "%Y-%m-%d", "date": "$_id" } },
    "count": { "$sum": 1 }
  }}
])

Try it here

And with the previous versions

db.collection.aggregate([
  { "$project": {
    "date": { "$add": [ new Date(0), "$_id" ] }
  }}
])