Question

i have a problem with auto incremental primary keys..

when im adding a student to my database, i can add the same student over and over again because the primary key of student is auto incremental so it is, of course, never repeated, i need to verify that the SSN of the student does not already exist in the database before inserting.

how can i do that on mvc3?? (im totally new in .net and mvc3)

my code for create in the student controller is:

[HttpPost]
    public ActionResult Create(Alumno alumno)
    {
        try
        {
            using (var db = new administracionEntities())
            {
                db.Alumno.Add(alumno);
                db.SaveChanges();
            }
            return RedirectToAction("Index");
        }
        catch
        {
            return View();
        }
    }

Answer 1

before you insert check if input alumno.ssn doesnot exist like

db.Alumno.where(a=> a.ssn == alumno.ssn).Any()

if this returns true, then there exists a ssn in database.

There are different ways in which you can achieve this in MVC.In one of which, You can have this call in a separate call to controller than in Create Action. May be you can check if duplicate SSN exists through JQuery.Ajax call on SSN textbox blur event on client side.

$.ajax({
   type: "Get",
   url: "StudentController/DoesSSNExist",
   data: "ssn=#", 
   success: function(msg){
       if(msg)
        alert('ssn already exists');
   }

This is controller action

public bool DoesSSNExist(string ssn)
{
    return db.Alumno.where(a=> a.ssn == ssn).Any()
}