How can I change the field name in MongoDB?

To change the field name, use the $project. Let us create a collection with documents −

> db.demo517.insertOne({"Name":"Chris Brown"});{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e88a2a2987b6e0e9d18f595")
}
> db.demo517.insertOne({"Name":"David Miller"});{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e88a2ab987b6e0e9d18f596")
}
> db.demo517.insertOne({"Name":"John Doe"});{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e88a2b1987b6e0e9d18f597")
}

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

> db.demo517.find();

This will produce the following output −

{ "_id" : ObjectId("5e88a2a2987b6e0e9d18f595"), "Name" : "Chris Brown" }
{ "_id" : ObjectId("5e88a2ab987b6e0e9d18f596"), "Name" : "David Miller" }
{ "_id" : ObjectId("5e88a2b1987b6e0e9d18f597"), "Name" : "John Doe" }

Following is the query to change the field name −

> db.demo517.aggregate([{$project:{FullName:"$Name"}}]);

This will produce the following output −

{ "_id" : ObjectId("5e88a2a2987b6e0e9d18f595"), "FullName" : "Chris Brown" }
{ "_id" : ObjectId("5e88a2ab987b6e0e9d18f596"), "FullName" : "David Miller" }
{ "_id" : ObjectId("5e88a2b1987b6e0e9d18f597"), "FullName" : "John Doe" }