Comparing objects before and after update retrieved by LINQ query - linq

Question

I am using LINQtoSQL and I need to compare object before and after update.
In the example below Student 'before' and Student 'curStudent' are the same, because they was retrieved by the same query.
using(DataContext db = new DataContext())
{
Student before = db.Student.Where(q=>q.id == 1).SingleOrDefault();
Student curStudent = db.Student.Where(q=>q.id == 1).SingleOrDefault();
curStudent.Name = "NewName";
db.SubmitChanges();
}
if(before.Name != curStudent.Name) // this condition will never be true
{
//do something
}

Answer 1

The context will only keep one object per key value, so one way would be to use two separate contexts:
Student before;
using(DataContext db1 = new DataContext())
{
before = db.Student.Where(q=>q.id == 1).SingleOrDefault();
}
Student curStudent;
using(DataContext db2 = new DataContext())
{
curStudent = db.Student.Where(q=>q.id == 1).SingleOrDefault();
curStudent.Name = "NewName";
db.SubmitChanges();
}
if(before.Name != curStudent.Name)
{
//do something
}
Or if you're just interested in the name change, keep the previous value:
string before;
using(DataContext db = new DataContext())
{
Student curStudent = db.Student.Where(q=>q.id == 1).SingleOrDefault();
before = curStudent.Name; // cache the name
curStudent.Name = "NewName";
db.SubmitChanges();
}
if(before != curStudent.Name)
{
//do something
}