How to use save() correctly in MongoDB?

Use the db.collection.save() to update an existing document or inserts a new document, depending on its document parameter. Let us create a collection with documents −

> db.demo481.save({"FirstName":"Chris","LastName":"Brown"});
WriteResult({ "nInserted" : 1 })
> db.demo481.save({"FirstName":"David","LastName":"Miller"});
WriteResult({ "nInserted" : 1 })
> db.demo481.save({"FirstName":"John","LastName":"Doe"});
WriteResult({ "nInserted" : 1 })
> db.demo481.save({"FirstName":"John","LastName":"Smith"});
WriteResult({ "nInserted" : 1 })

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

> db.demo481.find();

This will produce the following output −

{ "_id" : ObjectId("5e82db39b0f3fa88e227909c"), "FirstName" : "Chris", "LastName" : "Brown"
}
{ "_id" : ObjectId("5e82db45b0f3fa88e227909d"), "FirstName" : "David", "LastName" : "Miller"
}
{ "_id" : ObjectId("5e82db4db0f3fa88e227909e"), "FirstName" : "John", "LastName" : "Doe" }
{ "_id" : ObjectId("5e82db52b0f3fa88e227909f"), "FirstName" : "John", "LastName" : "Smith" }