Data type conversion in MongoDB

Question

I have a collection called Document in MongoDB. Documents in this collection have a field called CreationDate stored in ISO date type. My task is to count the number of docu

Answer 1

To convert date format to "xxxx-xx-xx"

db.getCollection('analytics').aggregate([
 {$project: {
     day: {$dayOfMonth: "$createdAt"},
     month: {$month: "$createdAt"},
     year: {$year: "$createdAt"},
     }
  },
  {$project: {
      day: {$concat:["0", {$substr:["$day",0, 2]}]},
     month: {$concat:["0", {$substr:["$month",0, 2]}]},
     year: {$substr:["$year",0, 4]},
      }
  },
  {$project: {date: {$concat: [{$substr:["$year",0, 4]},"-", {$substr:["$month",0, 2]},"-", {$substr:["$day",0, 2]}]}}},
]);