How to aggregate array documents in MongoDB?

For this, use the aggregate framework. Let us first create a collection with documents −

> db.aggregateArrayDemo.insertOne(    {       "_id":100,       "UserDetails": [          {             "UserName": "John",             "UserLoginYear":2010          },          {             "UserName": "Carol",             "UserLoginYear":2019          }       ]    } ); { "acknowledged" : true, "insertedId" : 100 }

Following is the query to display all documents from a collection with the help of find() method −

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

This will produce the following output −

{    "_id" : 100,    "UserDetails" : [       {          "UserName" : "John",          "UserLoginYear" : 2010       },       {          "UserName" : "Carol",          "UserLoginYear" : 2019       }    ] }

Following is the query to aggregate array documents −

> db.aggregateArrayDemo.aggregate([    {       $match: { _id: 100 }    },    {       $project: {          Minimum: { $min: "$UserDetails.UserLoginYear" },          Maximum: { $max: "$UserDetails.UserLoginYear" }       }    } ]);

This will produce the following output −

{ "_id" : 100, "Minimum" : 2010, "Maximum" : 2019 }