Static in asp.net mvc - asp.net-mvc

Question

I am learning Asp.net MVC.
I am building an application in which I have following components:
1.Student class:
public class Students
{
[Required(ErrorMessage="Student Id is required")]
[Display(Name="Student Id")]
public int Sid { get; set; }
[Required]
public string FirstName { get; set; }
[Required]
public string LastName { get; set; }
[Required]
public string Address { get; set; }
[DisplayFormat(ApplyFormatInEditMode = true, DataFormatString = "{0:yyyy-MM-dd}")]
[DataType(DataType.Date)]
public DateTime DOB { get; set; }
[Required]
public string Email { get; set; }
}
2.StudentManager class
public List<Students> sList = new List<Students>()
{
new Students{Sid=1001,FirstName="A",LastName="T",DOB=Convert.ToDateTime("14-10-1987"),Email="a#b.com",Address="I"},
new Students{Sid=1002,FirstName="B",LastName="U",DOB=Convert.ToDateTime("14-10-1987"),Email="a#b.com",Address="I"},
new Students{Sid=1003,FirstName="C",LastName="V",DOB=Convert.ToDateTime("14-10-1987"),Email="a#b.com",Address="I"},
new Students{Sid=1004,FirstName="D",LastName="W",DOB=Convert.ToDateTime("14-10-1987"),Email="a#b.com",Address="I"},
new Students{Sid=1005,FirstName="E",LastName="X",DOB=Convert.ToDateTime("14-10-1987"),Email="a#b.com",Address="I"},
new Students{Sid=1006,FirstName="F",LastName="Y",DOB=Convert.ToDateTime("14-10-1987"),Email="a#b.com",Address="I"},
new Students{Sid=1007,FirstName="G",LastName="Z",DOB=Convert.ToDateTime("14-10-1987"),Email="a#b.com",Address="I"},
};
public void Edit(Students s)
{
Students stud = sList.Where(st => st.Sid == s.Sid).First();
stud.FirstName = s.FirstName;
stud.LastName = s.LastName;
stud.Email = s.Email;
stud.DOB = s.DOB;
}
3. And a student controller
public static StudentManager sm = new StudentManager();
// GET: Student
public ActionResult Index()
{
return View(sm.sList);
}
public ActionResult Edit(int? id)
{
Students student = sm.sList.Where(s => s.Sid == id).First();
return View(student);
}
[HttpPost]
public ActionResult Edit(Students s)
{
sm.Edit(s);
return RedirectToAction("Index");
}
My queries are:
1.I am able to edit a student's details.But if I do not use the keyword static in Controller then it is not updating.
2.How Model Binding automatically passes Student object to HttpPost Edit()?
Can someone please explain?

Answer 1

Every time you create StudentManager class you are creating new collection of students.
When StudentManager is static it is created only once, so you ll use the same object for every call and modify collection in it.
When StudentManager is not static for every call you ll create new object with new collection, so your edit will modify collection within object that ll be thrown away with a next call (like view).
It's not a good practice to have references to dependencies as static properties. I would recommend to make you collection property static and initialize it only once for life cycle of application and later migrate to use db or file or a call, depending of what your goal is.
Model Binding uses one of the registered Model Binders, some are provided by default so for main types of data, like JSON, you don't have to to anything.
I would definitely recommend to read a good book about mvc, to get the mechanics behind it. As the good and the bad part about it is it works like "magic" =)