How do I order a list and add position to its items in MongoDB?

To order a list, use sort(). Let us create a collection with documents −

> db.demo581.insertOne({"Name":"Chris","Score":56});{
   "acknowledged" : true, "insertedId" : ObjectId("5e91cbbbfd2d90c177b5bcb6")
}
> db.demo581.insertOne({"Name":"Bob","Score":240});{
   "acknowledged" : true, "insertedId" : ObjectId("5e91cbbbfd2d90c177b5bcb7")
}
> db.demo581.insertOne({"Name":"David","Score":150});{
   "acknowledged" : true, "insertedId" : ObjectId("5e91cbbcfd2d90c177b5bcb8")
}

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

> db.demo581.find();

This will produce the following output −

{ "_id" : ObjectId("5e91cbbbfd2d90c177b5bcb6"), "Name" : "Chris", "Score" : 56 }
{ "_id" : ObjectId("5e91cbbbfd2d90c177b5bcb7"), "Name" : "Bob", "Score" : 240 }
{ "_id" : ObjectId("5e91cbbcfd2d90c177b5bcb8"), "Name" : "David", "Score" : 150 }

Following is the query to order a list and add position to its items in MongoDB −

> db.demo581.createIndex({Score:1})
{
   "createdCollectionAutomatically" : false,
   "numIndexesBefore" : 1,
   "numIndexesAfter" : 2,
   "ok" : 1
}
> var i = 1;
> db.demo581.find().sort({"Score": 1}).forEach(function (d){
...    d.Position = i;
...    i++;
...    db.demo581.save(d);
... })

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

> db.demo581.find();

This will produce the following output −

{ "_id" : ObjectId("5e91cbbbfd2d90c177b5bcb6"), "Name" : "Chris", "Score" : 56, "Position" : 1 }
{ "_id" : ObjectId("5e91cbbbfd2d90c177b5bcb7"), "Name" : "Bob", "Score" : 240, "Position" : 3 }
{ "_id" : ObjectId("5e91cbbcfd2d90c177b5bcb8"), "Name" : "David", "Score" : 150, "Position" : 2 }