In Edit method, updating data create new data instead mvc5 - asp.net-mvc-5

Question

This is my Controllers Edit Method in Httpost
[HttpPost]
public ActionResult Edit(Employee employee)
{
if (!ModelState.IsValid)
{
var department = db.Departments.ToList();
var viewModel = new EmployeeViewModel
{
Departments = department,
Employees = db.Employees.ToList()
};
return View("Index", viewModel);
}
db.Entry(employee).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
this method creates new data instead of updating data.

Answer 1

The problem is you're trying to update Employee instance directly based from action parameter without seeking any matching record first, hence EF "unaware" if the entity should be modified and treat its state as EntityState.Added in this line:
db.Entry(employee).State = EntityState.Modified;
What you should do is using SingleOrDefault() or FirstOrDefault() to fetch matching record based from Id property, update all required properties then attach Employee instance into Employees entity and set its state as EntityState.Modified:
[HttpPost]
public ActionResult Edit(Employee employee)
{
if (!ModelState.IsValid)
{
var department = db.Departments.ToList();
var viewModel = new EmployeeViewModel
{
Departments = department,
Employees = db.Employees.ToList()
};
return View("Index", viewModel);
}
// find employee with matching ID first
var selectedEmployee = db.Employees.SingleOrDefault(x => x.Id == employee.Id);
// update all properties
selectedEmployee.Name = employee.Name;
// other properties here
// attach the context
db.Employees.Attach(selectedEmployee);
// set modified state and save all changes
db.Entry(selectedEmployee).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
Related issues:
Why does Entity Framework reinsert existing objects into my database?
Updating the Record with EntityState.Modified but its inserting the new row rather than update