Why It showing error in modifying db in mvc in edit action

Question

I have a confution in my project that  when I am modifying the data to db it shows the error that "

Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. See http://go.microsoft.com/fwlink/?LinkId=472540 for information on understanding and handling optimistic concurrency exceptions."

 

I am getting the value which I needed in the HttpPost of edit action method, the error arise only when saving it to the db

controller

 

[HttpPost]

[ValidateAntiForgeryToken]

public async Task<ActionResult> Edit( StudentDetail studentDetail )

{

if (ModelState.IsValid)

{

studentDetail .CashInHand -= studentDetail .CashReceived;

studentDetail .Amount += studentDetail .CashReceived;

studentDetail .Date = DateTime.Now;

studentDetail .cashReceived = null;

db.Entry(studentDetail ).State = EntityState.Modified;

await db.SaveChangesAsync();

return RedirectToAction("Index");

}

return View(studentDetail );

}

 

 

I am getting details in  studentDetail. Then Why is that the error showing ???can anyone please help me to find the solution ??