linq to entity update records to database - asp.net

Question

This is the update code I found:
using (TestDBEntities ctx = new TestDBEntities())
{
//Get the specific employee from Database
Emp e = (from e1 in ctx.Emp
where e1.Name == "Test Employee"
select e1).First();
//Change the Employee Name in memory
e.Name = "Changed Name";
//Save to database
ctx.SaveChanges();
}
Now what I am doing is like this:
using(CRNNSTestEntities crnnsupContext = new CRNNSTestEntities())
{
CPersonalInfo t = ((IQueryable<CPersonalInfo>)Cache["personquery"]).First();
t.Tombstone.Address = Address1.Text;
System.Windows.Forms.MessageBox.Show(crnnsupContext.SaveChanges()+"");
};
which doesn't work. So my question is do I have to write something like CPersonalInfo t = from t in ....
Why doesn't my method doesn't work?
Thanks

Answer 1

You need to get the entity CPersonalInfo t from your crnnsupContext and not from your Cache

Answer 2

You can also attach object to the context before.
More info how to use attach here

Answer 3

can you change this
using (TestDBEntities ctx = new TestDBEntities())
{
//Get the specific employee from Database
Emp e = (from e1 in ctx.Emp
where e1.Name == "Test Employee"
select e1).First();
//Change the Employee Name in memory
e.Name = "Changed Name";
//Save to database
ctx.SaveChanges();
}
into
using (TestDBEntities ctx = new TestDBEntities())
{
//Get the specific employee from Database
Emp e = (from e1 in ctx.Emp
where e1.Name == "Test Employee"
select e1).First();
var entity = ctx.Emp.Find(e);
//Change the Employee Name in memory
entity.Name = "Changed Name";
//Save to database
ctx.SaveChanges();
}