DbContext object not working from within loop

Question

Here is my ActionMethod, it does not populate data to database.

private StudentDBContext db = new StudentDBContext();

public ActionResult PopulateData()
        {
            Student objStu = new Student();

            for(int i=0;i<2;i++)
            {
                objStu.ID = i+1;
                objStu.name = "something";
                db.Students.Add(objStu);
                db.SaveChanges();
            }


            return View();
        }

Only time when it does is when I use it without loop(as shown below) why is that so?

public ActionResult PopulateData()
        {
            Student objStu = new Student();

            //for(int i=0;i<2;i++)
            //{
                objStu.ID = 1;
                objStu.name = "something";
                db.Students.Add(objStu);
                db.SaveChanges();
            //}


            return View();
        }

try putting Student objStu = new Student(); inside the loop. — Tarec
– Tarec, Commented Jul 8, 2014 at 17:40
You don't get any updates with the loop or you only get one update with the loop? — Mike Cheel
– Mike Cheel, Commented Jul 8, 2014 at 17:41
I would think your original code would first add a student to the database and then the second time through the loop it would update the first record it put in. Is that not happening? — Mike Cheel
– Mike Cheel, Commented Jul 8, 2014 at 17:45

Eric Scherrer · Accepted Answer · 2014-07-08 17:46:57Z

6

You are adding the same student over and over again. Instead, create the new student (objStu) inside the loop:

public ActionResult PopulateData()
{        
    for(int i=0;i<2;i++)
    {
        Student objStu = new Student();
        objStu.ID = i+1;
        objStu.name = "something";
        db.Students.Add(objStu);
    }

    db.SaveChanges();

    return View();
}

edited Jul 8, 2014 at 17:46

answered Jul 8, 2014 at 17:40

Eric Scherrer

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1 Comment

L_7337 Over a year ago

This is because when you add the objStu object to the context, it is "tracked". Any future changes to this object will be persisted with db.SaveChanges() is called.

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