Get fields from multiple sub-documents that match a condition in MongoDB?

To get fields from multiple sub-documents, use MongoDB aggregate with $unwind. Let us create a collection with documents −

> db.demo671.insertOne( ... { ... ...    "details" : [ ...    { ...       "id" : "1" ...    }, ...    { ...       CountryName:"US", ...       "details1" : [ ...       { ...       "id" : "1" ...       }, ...       { ...          "id" : "2" ...       } ...       ] ... }, ... { ...    CountryName:"UK", ...    "details1" : [ ...    { ...       "id" : "2" ...    }, ...    { ...       "id" : "1" ...    } ...    ] ... }, ... { ...    CountryName:"AUS", ...    "details1" : [ ...       { ...          "id" : "1" ...       } ...       ] ...    } ... ] ... } ... ) {    "acknowledged" : true,    "insertedId" : ObjectId("5ea3e5d004263e90dac943e0") }

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

> db.demo671.find();

This will produce the following output −

{ "_id" : ObjectId("5ea3e5d004263e90dac943e0"), "details" : [ { "id" : "1" }, { "CountryName" : "US", "details1" : [ { "id" : "1" }, { "id" : "2" } ] }, { "CountryName" : "UK", "details1" : [ { "id" : "2" }, { "id" : "1" } ] }, { "CountryName" : "AUS", "details1" : [ { "id" : "1" } ] } ] }

Here is the query to get fields from multiple sub-documents that match a condition in MongoDB −

> db.demo671.aggregate([ ... ...   {$unwind: '$details'}, ... ...   {$match: {'details.details1.id': '1'}}, ... ... {$project: {_id: 0, Country: '$details.CountryName'}} ... ]).pretty()

This will produce the following output −

{ "Country" : "US" } { "Country" : "UK" } { "Country" : "AUS" }