C # driver 2.0 Mongodb UpdateOneAsync

Question

`

public class Student
{
    public long StudentId {get; set;}
    public string Fname {get; set;}
    public string Lname {get; set;}
    public List<ObjectId> CoursesList {get; set;}
    public int IQ {get;set;}
}

public class Courses
{
    [BsonId]
    public ObjectId Id { get; set; }
    public string CourseNumber{get; set;}
    public string CourseName{get; set;}
}

`

How to add / add the cursor identifier to the list of courses (which may be empty for the first time) of the Student object

PS: I know how to set the field using the command below. I hope this will be the same for the above problem.

await StudentCollection.UpdateOneAsync(a => a.StudentId == studentId, Builders<Student>.Update.Set( a => a.IQ,90));

Answer 1

As you already discovered, C # code to use $ addToSet:

var filter = Builders<Student>.Filter.Eq(s => s.StudentId, studentId);
var update = Builders<Student>.Update.AddToSet(s => s.CoursesList, courseId);
var result = await collection.UpdateOneAsync(filter, update);

However, $ addToSet will not work if the CourseList member was saved in the collection as null. The server requires that the existing value for $ addToSet be an array (this may be an empty array).

The easiest solution is to just keep an empty list for CoursesList instead of null when there are no courses.

Answer 2

. "", , AddToSet/Push.

public List<ObjectId> CoursesList = new List<ObjectId>();