context.SaveChanges() not persisting data in database - sql-server

Question

Im working on a MVC app.
When I call context.SaveChanges to update a specific records. The update is not registered in the database. I do not get any runtime error either. All in notice is that my Records is not updated. I still see the same values. Insert Functionality work Perfectly.
enter code here
public Admission Update(int stuid){
VDData.VidyaDaanEntities context = new VDData.VidyaDaanEntities();
VDData.Student_Master studentmaster = new VDData.Student_Master();
studentmaster.Student_ID = stuid;
studentmaster.Student_First_Name = this.FirstName;
studentmaster.Student_Middle_Name = this.MiddleName;
studentmaster.Student_Last_Name = this.LastName;
studentmaster.Student_Address_1 = this.Address;
studentmaster.Student_Address_2 = this.Address2;
studentmaster.Student_City = this.City;
studentmaster.Student_State = this.State;
studentmaster.Student_Pin_Code = this.Pincode;
context.SaveChanges(); // here it wont give any kind of error. it runs sucessfully. }

Answer 1

First get the entity you are going to update:
var entity = obj.GetEntity(id);
entity.col1 = "value";
context.SaveChanges(entity);
hope this will help.

Answer 2

It seems like you want to update, so your code should be
VDData.Student_Master studentmaster = context.Student_Masters.Single(p=>p.Student_ID == stuid);
And you should not change the Student_ID if it is the primary key.
public Admission Update(int stuid){
VDData.VidyaDaanEntities context = new VDData.VidyaDaanEntities();
//VDData.Student_Master studentmaster = new VDData.Student_Master();
//REPLACE WITH
VDData.Student_Master studentmaster = context.Student_Masters.Where(p=>p.Student_ID == stuid);
studentmaster.Student_ID = stuid;
studentmaster.Student_First_Name = this.FirstName;
studentmaster.Student_Middle_Name = this.MiddleName;
studentmaster.Student_Last_Name = this.LastName;
studentmaster.Student_Address_1 = this.Address;
studentmaster.Student_Address_2 = this.Address2;
studentmaster.Student_City = this.City;
studentmaster.Student_State = this.State;
studentmaster.Student_Pin_Code = this.Pincode;
context.SaveChanges();

Answer 3

Before
context.SaveChanges();
You need to call this
context.Student_Masters.Add(studentmaster );
Edit: introduce Abstraction to your Context class and Create a method in your context class like below, then you can call it whenever you want to create or update your objects.
public void SaveStudent_Master(Student_Master studentmaster)
{
using (var context = new VDData.VidyaDaanEntities())
{
if (studentmaster.Student_ID == 0)
{
context.Student_Masters.Add(studentmaster);
}
else if (studentmaster.Student_ID > 0)
{
//This Updates N-Level deep Object grapgh
//This is important for Updates
var currentStudent_Master = context.Student_Masters
.Single(s => s.Student_ID == studentmaster.Student_ID );
context.Entry(currentStudent_Master ).CurrentValues.SetValues(studentmaster);
}
context.SaveChanges();
}
Then in your Controller replace context.SaveChanges(); with _context.SaveStudent_Master(studentmaster);