mongodb - convert iso date to timestamp in mongo query

Question

here is the query

[
    { 
        "$project": {
            "formattedDate": { 
                "$dateToString": { "format": "%Y-%m-%d", "date": "$ceatedAt" } 
            },
            "createdAtMonth": { "$month": "$ceatedAt" },
            "rating": 1
        }
    },
    {
         "$group": {
             "_id": "$formattedDate",
             "average": { "$avg": "$rating" },
             "month": { "$first": "$createdAtMonth" },
         }
    }
]

I need the date in timestamp. How to do that?

Answer 1

Mongodb 4.0 has introduced $toLong aggregation which convert date to timestamp

db.collection.aggregate([
  { "$project": {
    "createdAt": {
      "$toLong": "$createdAt"
    }
  }}
])

You can try it here