Update List column values, if value is null using Linq

Question

I have List<Student> with multiple records

public class Student
{            
    public int? StudentId { get; set; }
    public string StudentName { get; set; }
    public int? AttendanceStatusId { get; set; }
    public string AttendanceStatusDes { get; set; }     
}

While posting data to server, sometimes AttendanceStatusId & AttendanceStatusDes going null. When these 2 values are null in List records, I want to set AttendanceStatusId=1 & AttendanceStatusDes="Present" How could I do that using Linq query. Thank you

What have you tried? Why do you think a language-integrated query (that´s what linq stands for) would be the way to do this? Simply use a loop instead. — MakePeaceGreatAgain
– MakePeaceGreatAgain, Commented Jul 24, 2018 at 7:12
Why not just add a backing field for to the property and if this is null return 1 in the getter of AttendanceStatusId. — Martin Backasch
– Martin Backasch, Commented Jul 24, 2018 at 7:13
I am getting all records from server along with values so now I need to set the values. I tried loops but I though there might be easy solution using linq Thank you. — Arvind Chourasiya
– Arvind Chourasiya, Commented Jul 24, 2018 at 7:15
Don´t overcomplicate things with a technnique that isn´t made for updates but for querying. Just stay with your solution unless you have a real problem with it. — MakePeaceGreatAgain
– MakePeaceGreatAgain, Commented Jul 24, 2018 at 7:16

Renatas M. · Accepted Answer · 2018-07-24 08:55:47Z

7

Instead of using LINQ or loops, set defaults for your model. This way you will be always sure you get your model as expected and you don't need to mess around everywhere with all your list of Students.

This might not be applicable for OPs case but worth to mention, that using this "technique" you still get default values if your class is serializable.

public class Student
{
    public int? StudentId { get; set; }
    public string StudentName { get; set; }
    private int? _attendanceStatusId;
    public int? AttendanceStatusId
    {
        //you can use null coalescing operator here
        //like this: get { return _attendanceStatusId ?? 1; }
        get { return _attendanceStatusId == null ? 1 : _attendanceStatusId; }
        set { _attendanceStatusId = value; }
    }
    private string _attendanceStatusDes;
    public string AttendanceStatusDes
    {
        //Or get { return _attendanceStatusDes ?? "Present" }
        get { return _attendanceStatusDes == null ? "Present" : _attendanceStatusDes; }
        set { _attendanceStatusDes = value; }
    }
}

edited Jul 24, 2018 at 8:55

answered Jul 24, 2018 at 7:17

Renatas M.

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8 Comments

MakePeaceGreatAgain Over a year ago

Definitly the best answer.

Nino Over a year ago

or to make it a bit simpler :) get { _attendanceStatusId ?? 1 }

Renatas M. Over a year ago

@Nino I agree. I just wanted to show the null check in simple form. :) I will add it as comment.

Guy Over a year ago

public int? AttendanceStatusId { get; set; } = 1; will also do the trick.

Renatas M. Over a year ago

@Guy If you accidentally set property to null it will no longer return 1.

|

Mafii · Accepted Answer · 2018-07-24 07:15:27Z

1

Get the filtered list:

var missingStatus = Students.Where(s => !s.AttendanceStatusId.HasValue && AttendanceStatusDes == null);

And then iterate over that list, editing the values on these items.

foreach(var student in missingStatus)
{
  student.AttendanceStatusId = 1;
  student.AttendanceStatusDes = "Present";
}

Does that help?

You can of course do it in a foreach on a list, but I don't recomment that:

Students.Where(s => !s.AttendanceStatusId.HasValue && AttendanceStatusDes == null)
  .ToList()
  .ForEach(s => {
      s.AttendanceStatusId = 1;
      s.AttendanceStatusDes = "Present";
  });

answered Jul 24, 2018 at 7:15

Mafii

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Comments

Maciej Pulikowski · Accepted Answer · 2018-07-24 07:22:50Z

1

Just set default value, If you are using C# 6+ you can do this:

class Student
{
    public int? StudentId { get; set; }
    public string StudentName { get; set; }
    public int AttendanceStatusId { get; set; } = 1;
    public string AttendanceStatusDes { get; set; } = "Present";
}

answered Jul 24, 2018 at 7:22

Maciej Pulikowski

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Comments

Umang · Accepted Answer · 2018-07-24 07:25:14Z

1

I think I would go with following:

Students.Select(t=>new Student{
AttendanceStatusId = t.AttendanceStatusId.HasValue?t.AttendanceStatusId.Value:1, 
AttendanceStatusDes = t.AttendanceStatusId.HasValue?t.AttendanceStatusDes : "Present" , 
StudentId = t.StudentId,
StudentName = t.StudentName
});

answered Jul 24, 2018 at 7:25

Umang

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Comments

Gautham Srinivasan · Accepted Answer · 2018-07-24 07:47:19Z

[Route("api/Sample/Murugan")]
        [HttpGet]
        public string Name()
        {
            List<Student> obj = new List<Student> {
                new Student { AttendanceStatusDes=null, AttendanceStatusId =null, StudentId =1, StudentName ="A" },
                new Student { AttendanceStatusDes="", AttendanceStatusId =1, StudentId =2, StudentName ="B" },
                new Student { AttendanceStatusDes="", AttendanceStatusId =2, StudentId =3, StudentName ="C" },
                new Student { AttendanceStatusDes=null, AttendanceStatusId =null, StudentId =4, StudentName ="D" },
            };

            for (int Count = 0; Count < obj.Count(); Count++)
            {
                if (obj[Count].AttendanceStatusId == null && obj[Count].AttendanceStatusDes == null)
                {
                    obj[Count].AttendanceStatusId = 1;
                    obj[Count].AttendanceStatusDes = "Present";
                }
            }
            return "Muruganvc";
        }

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