$addFields:

In MongoDB, the $addFields operator is used in the MongoDB Shell (mongo shell) as part of the aggregation framework. 

It allows you to add new fields or computed fields to the documents in a collection during the aggregation pipeline.


The $addFields operator takes an object as its argument, where each field represents the name of the field to add or modify and its associated value.

 The values can be either a constant value or an expression that evaluates to a value.


Here's an example of how you can use $addFields in the MongoDB Shell:

db.collection.aggregate([
  {
    $addFields: {
      newField: "some value"} }
])

In this example, the $addFields stage adds three new fields to the documents in the collection:


newField: This field is assigned a constant value of "some value" for all documents.


After the $addFields stage, the resulting documents will contain the original fields from the collection, along with the newly added fields.


It's important to note that the $addFields operator does not modify the original documents in the collection but rather creates new fields in the aggregation output. 

If you want to modify existing fields, you can use other operators like $set or $project in the pipeline.


That's the basic usage of the $addFields operator in the MongoDB Shell. 

It allows you to add or modify fields in documents during the aggregation process, providing flexibility in transforming and enriching your data.

Example:

  Adding new field (email)