Aggregation: group date in nested documents (nested object) and display the count?

For aggregation, use aggregate() in MongoDB. Group the dates with $group. Let us create a collection with documents −

> db.demo717.insertOne( ...    { ...       "shippingdetails": ...       [ ...          { ...             duedate:"2020-04-29 22:33:04", ...          }, ...          { ...             duedate:"2020-03-29 22:33:04", ...          }, ...          { ...             duedate:"2020-04-29 22:33:04", ...          }, ...          { ...             duedate:"2020-01-29 22:33:04", ...          } ...       ] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea9b3cd85324c2c98cc4c30") }

Display all documents from a collection with the help of find() method −

> db.demo717.find().pretty();

This will produce the following output −

{    "_id" : ObjectId("5ea9b3cd85324c2c98cc4c30"),    "shippingdetails" : [       {          "duedate" : "2020-04-29 22:33:04"       },       {          "duedate" : "2020-03-29 22:33:04"       },       {          "duedate" : "2020-04-29 22:33:04"       },       {          "duedate" : "2020-01-29 22:33:04"       }    ] }

Following is the query for aggregation to group date in nested documents (nested object) −

> db.demo717.aggregate( ...    { ...       $unwind:"$shippingdetails"}, ...       { ...          $group: { ...             _id: "$shippingdetails.duedate", ...          count: { ...             $sum: 1 ...          } ...       } ...    } ... )

This will produce the following output −

{ "_id" : "2020-01-29 22:33:04", "count" : 1 } { "_id" : "2020-03-29 22:33:04", "count" : 1 } { "_id" : "2020-04-29 22:33:04", "count" : 2 }