You can use positional operator $ for this. To understand the above concept, let us create a collection with the document. The query to create a collection with a document is as follows −
> db.incrementValueInNestedArrayDemo.insertOne( ... {"UniqueId":1, ... "StudentDetails": ... [ ... { ... "StudentId":101, ... "StudentMarks":97 ... }, ... { ... "StudentId":103, ... "StudentMarks":99 ... }, ... { ... "StudentId":105, ... "StudentMarks":69 ... }, ... { ... "StudentId":107, ... "StudentMarks":59 ... } ... ] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5c77dd71fc4e719b197a12f7") }
Display all documents from a collection with the help of find() method. The query is as follows −
> db.incrementValueInNestedArrayDemo.find().pretty();
The following is the output −
{ "_id" : ObjectId("5c77dd71fc4e719b197a12f7"), "UniqueId" : 1, "StudentDetails" : [ { "StudentId" : 101, "StudentMarks" : 97 }, { "StudentId" : 103, "StudentMarks" : 99 }, { "StudentId" : 105, "StudentMarks" : 92 }, { "StudentId" : 107, "StudentMarks" : 59 } ] }
Here is the query to increment a value in the nested array −
> db.incrementValueInNestedArrayDemo.update({UniqueId:1,"StudentDetails.StudentId":107}, {$inc:{"StudentDetails.$.StudentMarks":1}}); WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
Let us check nested array value is incremented or not in the above collection with StudentId 107 −
> db.incrementValueInNestedArrayDemo.find().pretty();
The following is the output −
{ "_id" : ObjectId("5c77dd71fc4e719b197a12f7"), "UniqueId" : 1, "StudentDetails" : [ { "StudentId" : 101, "StudentMarks" : 97 }, { "StudentId" : 103, "StudentMarks" : 99 }, { "StudentId" : 105, "StudentMarks" : 92 }, { "StudentId" : 107, "StudentMarks" : 60 } ] }
Look at the sample output, the field name “StudentMarks” has been updated from 59 to 60 that means increments by 1.