How to update record in MongoDB without replacing the existing fields?

You can use $set operator for this Let us first create a collection with documents −

> db.updateRecordDemo.insertOne({"StudentName":"Larry"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbd6f95de8cc557214c0e0a") } > db.updateRecordDemo.insertOne({"StudentName":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbd6f9cde8cc557214c0e0b") } > db.updateRecordDemo.insertOne({"StudentName":"Mike"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5cbd6f9dde8cc557214c0e0c") }

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

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

This will produce the following output −

{ "_id" : ObjectId("5cbd6f95de8cc557214c0e0a"), "StudentName" : "Larry" } { "_id" : ObjectId("5cbd6f9cde8cc557214c0e0b"), "StudentName" : "David" } { "_id" : ObjectId("5cbd6f9dde8cc557214c0e0c"), "StudentName" : "Mike" }

Following is the query to update record in MongoDB without replacing the existing fields −

> db.updateRecordDemo.update({"_id" :ObjectId("5cbd6f9cde8cc557214c0e0b") },{$set : {"StudentAge":24}});    WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

Let us Display all documents from the collection once again −

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

This will produce the following output −

{ "_id" : ObjectId("5cbd6f95de8cc557214c0e0a"), "StudentName" : "Larry" } {    "_id" : ObjectId("5cbd6f9cde8cc557214c0e0b"),    "StudentName" : "David",    "StudentAge" : 24 } { "_id" : ObjectId("5cbd6f9dde8cc557214c0e0c"), "StudentName" : "Mike" }