MongoDB aggregation to fetch documents with specific field value?

For this, use aggregate(). Let’s say we have to fetch documents with a field “Age” with value “21”.

Let us now create a collection with documents −

> db.demo685.insertOne( ...    { ...       "details": ...       [ ...          { ...             Name:"Chris", ...             Age:21 ...          }, ...          { ...             Name:"David", ...             Age:23 ...          }, ...          { ...             Name:"Bob", ...             Age:21 ...          } ...       ] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea54f6fa7e81adc6a0b395b") }

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

> db.demo685.find();

This will produce the following output −

{ "_id" : ObjectId("5ea54f6fa7e81adc6a0b395b"), "details" : [    { "Name" : "Chris", "Age" : 21 },    { "Name" : "David", "Age" : 23 },    { "Name" : "Bob", "Age" : 21 } ] }

Following is the query for MongoDB aggregation −

> db.demo685.aggregate([ { $unwind: "$details" }, { $match: { "details.Age": 21 } }, { $project: {_id: 0}} ]).pretty();

This will produce the following output −

{ "details" : { "Name" : "Chris", "Age" : 21 } } { "details" : { "Name" : "Bob", "Age" : 21 } }