What is the method for adding fields in MongoDB?

In MongoDB, you can use the $set operator to add fields. The specific syntax is as follows:

db.collection.updateOne(filter, update, options)

In this, collection represents the name of the set, filter represents the query criteria for matching documents, update represents the update operation to be performed, and options represent the update options.

To add a field, you can use the $set operator in the update parameter and specify the field and its value to be added. For example, to add a field named age to all documents in the collection named users, you can use the following code:

db.users.update({}, {$set: {age: 25}}, {multi: true})

This will add a field named age with a value of 25 to all documents in the users collection. Note that by passing an empty object {} as the filter parameter, you can match all documents.

If you want to add multiple fields, simply specify multiple fields and their values in the $set operator. For example, to add both age and gender fields at the same time, you can use the following code:

db.users.update({}, {$set: {age: 25, gender: 'male'}}, {multi: true})

This will add fields for age and gender to all documents, with their values set to 25 and ‘male’ respectively.

If you only want to add a field to the first matching document, you can use the updateOne method. For example, to add a field called age to the first document in a collection named users, you can use the following code:

db.users.updateOne({}, {$set: {age: 25}})