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 do I add/append a courser Id to Course list(which may be null for the first time) of a Student object

PS: I know how to set a field using the below command. I am hoping it is on similar lines for the above problem

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

You mean something like this: Builders<Student>.Update.Set( a => a.CourseList, new []{ObjectId}) — Peyman
– Peyman, Commented Apr 14, 2015 at 22:57
more like Builders<Student>.Update.AddToSet( a => a.CourseList, newCourse.Id}) where newCourse is the newly course object created and I am trying to append its course Id into that course list of student object — user1789710
– user1789710, Commented Apr 15, 2015 at 0:27
Builders<Student>.Update.AddToSet( a => a.CourseList, new []{newCourse.Id}) — Peyman
– Peyman, Commented Apr 15, 2015 at 0:44

Robert Stam · Accepted Answer · 2015-04-15 16:31:11Z

17

As you've already discovered, the C# code to use $addToSet is:

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 is not going to work if the CourseList member has been stored in the collection as a null. The server requires that the existing value for $addToSet be an array (it can be an empty array).

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

answered Apr 15, 2015 at 16:31

Robert Stam

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1 Comment

user1789710 Over a year ago

storing empty list to start with then using Builders<Student>.Update.AddToSetEach(s => s.CoursesList, courseList); worked for me. I think i didn't mention clearly in my question that i wanted add/append a new course list created. Thanks !

fatihyildizhan · Accepted Answer · 2015-05-09 15:59:53Z

0

This is working for me. When you define "List" like this, it will be empty and works with AddToSet/Push methods.

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

answered May 9, 2015 at 15:59

fatihyildizhan

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Comments

Marcel N. · Accepted Answer · 2020-05-22 08:46:30Z

0

The only case that you have to pay attention is when the array CourseList is null, in this case you have to use the code below (see also here):

var newListOfObject = new List<ObjectId>(){...}
await StudentCollection.UpdateOneAsync(a => a.StudentId == studentId, Builders<Student>.Update.Set( a => a.CoursesList, newListOfObject));

Otherwise you can use AddToSet or Push like explain in the other answers.

edited May 22, 2020 at 8:46

Marcel N.

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answered Jan 26, 2020 at 1:26

Ivan Cipriani

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