How can I update child objects in MongoDB?

To update child objects, use $set operator. Let us first create a collection with document −

>db.updateChildObjectsDemo.insertOne({"StudentName":"Chris","StudentOtherDetails":{"StudentSubject":"MongoDB","StudentCountryName":"AUS"}});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5ce964e078f00858fb12e91f")
}

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

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

This will produce the following output −

{
   "_id" : ObjectId("5ce964e078f00858fb12e91f"),
   "StudentName" : "Chris",
   "StudentOtherDetails" : {
      "StudentSubject" : "MongoDB",
      "StudentCountryName" : "AUS"
   }
}

Following is the query to update child objects in MongoDB −

> db.updateChildObjectsDemo.update({"StudentName" : "Chris"},{$set:{"StudentOtherDetails.StudentCountryName":"UK"}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

Let us check the document once again −

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

This will produce the following output −

{
   "_id" : ObjectId("5ce964e078f00858fb12e91f"),
   "StudentName" : "Chris",
   "StudentOtherDetails" : {
      "StudentSubject" : "MongoDB",
      "StudentCountryName" : "UK"
   }
}