Add new field to every document in a MongoDB collection?

To add new field to every document in a MongoDB collection, you can use $set operator. The syntax is as follows:

db.yourCollectionName.update({}, { $set: {"yourFieldName": yourValue} }, false, true);

To understand the above syntax, let us create a collection with some documents. The query to create a collection with documents is as follows:

>db.addNewFieldToEveryDocument.insertOne({"StudentName":"John","StudentAddress":"US "}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c6efc0b6fd07954a48906ae") } >db.addNewFieldToEveryDocument.insertOne({"StudentName":"David","StudentAddress":"U K"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c6efc0b6fd07954a48906af") } >db.addNewFieldToEveryDocument.insertOne({"StudentName":"Carol","StudentAddress":"U K"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c6efc0b6fd07954a48906b0") } >db.addNewFieldToEveryDocument.insertOne({"StudentName":"Bob","StudentAddress":"US" }); {    "acknowledged" : true,    "insertedId" : ObjectId("5c6efc0b6fd07954a48906b1") }

Display all documents from a collection with the help of find() method. The query is as follows:

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

The following is the output:

{    "_id" : ObjectId("5c6efc0b6fd07954a48906ae"),    "StudentName" : "John",    "StudentAddress" : "US" } {    "_id" : ObjectId("5c6efc0b6fd07954a48906af"),    "StudentName" : "David",    "StudentAddress" : "UK" } {    "_id" : ObjectId("5c6efc0b6fd07954a48906b0"),    "StudentName" : "Carol",    "StudentAddress" : "UK" } {    "_id" : ObjectId("5c6efc0b6fd07954a48906b1"),    "StudentName" : "Bob",    "StudentAddress" : "US" }

The following is the query to add a new field to every document:

> db.addNewFieldToEveryDocument.update({}, { $set: {"StudentAge": 24} }, false, true); WriteResult({ "nMatched" : 4, "nUpserted" : 0, "nModified" : 4 })

Above, we have added a new field “StudentAge”:24 in every document. Let us check the field “StudentAge”:24 is successfully added to every document or not. The query is as follows:

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

The following is the output:

{    "_id" : ObjectId("5c6efc0b6fd07954a48906ae"),    "StudentName" : "John",    "StudentAddress" : "US",    "StudentAge" : 24 } {    "_id" : ObjectId("5c6efc0b6fd07954a48906af"),    "StudentName" : "David",    "StudentAddress" : "UK",    "StudentAge" : 24 } {    "_id" : ObjectId("5c6efc0b6fd07954a48906b0"),    "StudentName" : "Carol",    "StudentAddress" : "UK",    "StudentAge" : 24 } {    "_id" : ObjectId("5c6efc0b6fd07954a48906b1"),    "StudentName" : "Bob",    "StudentAddress" : "US",    "StudentAge" : 24 }