Invoke SaveChanges two times in one transaction - asp.net-mvc

Question

all, I'm new here. My problem is how to invoke savechanges two times in one transaction.
Below is my code:
var order = new Order();
// modify order's properties
db.orders.add(order);
db.SaveChanges();
db.Entry(order).reload();
// do some other work about the order entity
db.Entry(order).state = EntityState.Modified;
db.SaveChanges();
But the second SaveChanges failed. The error message is "affects the unexpected number of rows (0).The entity may be modified or deleted after loading.Refresh ObjectStateManager".
My question is how to make the second SaveChanges() works. Because the property code in order entity is an autoincrease custom string field base on a custom function in database.
Thanks

Answer 1

Your call to .Reload() is not needed, and as #maxlego mentioned setting the .State to modified should not be needed if you haven't changed AutoDetectChangesEnabled from its default of true.
You should be able to follow this pattern and get the desired result. You can do the following with or without the TransactionScope. The benefit of using TransactionScope is that if your second call to SaveChanges() fails with an exception then the changes made by the first call will be rolled back. On the other hand, if you want the first call of SaveChanges() to succeed even when the second call fails you should remove the TransactionScope code.
using (var db = new MyContext())
using (var scope = new TransactionScope())
{
var order = new Order();
// modify order's properties
db.orders.add(order);
db.SaveChanges();
// make additional changes...
// E.g. assuming order.ID is an auto-incrementing primary key
// that is determined by the database I can now use the
// value the database set to log this change...
// save changes
db.SaveChanges();
// commit the transaction
scope.Complete();
}