Need to compare Value.From other table

Malcom Graves

i have 3 classes in my model

Model

public class Student
{
public int id { get; set; }
[Required]
[DisplayName("Student Name")]
public string Name { get; set; }
[Required]
public int RollNO { get; set; }
public DateTime EnrollmentDate { get; set; }
public ICollection Records { get; set; }
}
public class Record
{
public int Id { get; set; }
public int StudentId { get; set; }
public int SubjectId { get; set; }
[Required]
public int Marks { get; set; }
public string Result { get; set; }
public virtual Student Students { get; set; }
public virtual Subject Subjects { get; set; }
}
public class Subject
{
public int id { get; set; }
[Required]
public string Title { get; set; }
[Required]
[DisplayName("Minimum Marks")]
public int MinMarks { get; set; }
[Required]
[DisplayName("Max Marks")]
public int MaxMarks { get; set; }
public ICollection Records { get; set; }
}

In subject table i will be creating each subject and setting its minimum and maximum marks required to pass...now in record table (Create Page) i want to compare the selected subject minimum marks with Record.Marks and if its less the minimum marks get Fail in Record.Result and if its greater then maximum marks get Pass in Record.Result...and i also want to compare the Result.Marks property with Subject.MaxMarks and if its greater then Subject.MaxMarks the user should get and error in any form possible...

This is my controller

public ActionResult Create([Bind(Include = "Id,StudentId,SubjectId,Marks,Result")] Record record,Subject subject)
{
if(record.Marks
{
record.Result = "Fail";
}
else
{
record.Result = "Pass";
}
if (ModelState.IsValid)
{
db.Records.Add(record);
db.SaveChanges();
return RedirectToAction("Index");
}
ViewBag.StudentId = new SelectList(db.Students, "id", "Name", record.StudentId);
ViewBag.SubjectId = new SelectList(db.Subjects, "id", "Title", record.SubjectId);
return View(record);
}

3 Replies

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Mukesh Nayak8y ago
Check the value of record.subjectID . You should have data in Subject table and Student Table. selectedSubject can only be null if record.SubjectID doesn't exist in subject table. Its working fine for me though i have used database first approach.
Malcom Graves8y ago
its not working...getting an error.

System.NullReferenceException: 'Object reference not set to an instance of an object.'

selectedSubject was null.
Mukesh Nayak8y ago
Hi Malcom

I think you can do it like following:
var selectedSubject = db.Subjects.Where(sub => sub.ID == record.SubjectID).FirstOrDefault();
record.Result = record.Marks < selectedSubject.MinMarks ? "Fail" : "Pass";
if(record.Marks > selectedSubject.MaxMarks)
{
ModelState.AddModelError("Marks", "Given mark is greater than maximum mark");
}
if (ModelState.IsValid)
{
db.Records.Add(record);
db.SaveChanges();
return RedirectToAction("Index");
}
ViewBag.StudentID = new SelectList(db.Students, "ID", "Name", record.StudentID);
ViewBag.SubjectID = new SelectList(db.Subjects, "ID", "Title", record.SubjectID);
return View(record);