How to use $ positional operator in MongoDB C# driver version 2

Question

I need to update a field of one element from array sub document of a document.

MongoDB have the $ positional operator to do this. But in MongoDB C# driver version 2 it seems that there is no support for this operator.

How can I achieve this?

Documents:

{ "_id" : 1, "grades" : [ 80, 85, 90 ] }
{ "_id" : 2, "grades" : [ 88, 90, 92 ] }
{ "_id" : 3, "grades" : [ 85, 100, 90 ] }

Expected query:

db.students.update(
     { _id: 1, grades: 80 },
     { $set: { "grades.$" : 82 } }
   )

Meuse

Answer 1

You can try something like this.

var builder = Builders<Student>.Filter;
var filter = builder.Eq(student=> student.Id, 1) & builder.ElemMatch(student => student.Grades, x => x == 80);

var builder = Builders<Student>.Update;
var update = builder.Set(student => student.Grades[-1], 82);

var result = collection.UpdateOne(filter, update);

Whisker

Answer 2

I know this is a very late answer, but if anyone else comes across this I tried s7vr's answer with the -1 index and got an exception that pointed to Mongo's FirstMatchingElement method, and that solved my problem.

So it would be the same filter as in that answer, but replacing update with something like

var update = Builders<Student>.Update.Set(student => student.Grades.FirstMatchingElement(), 82);

Rosol