MVC Repositiry Pattern

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MVC

Hi, I am developing simple task using different layers and everything is working fine but I have scenario where I need to insert to two tables when click on save ,one employee table and other employeeposition table. Here is my code.
In Service class

public void Update(EmployeeViewModel employeeViewModel)
        {
            Employee employee = new Employee()
            {
                EmployeeId = employeeViewModel.EmployeeId,
                FirstName = employeeViewModel.FirstName,
                LastName = employeeViewModel.LastName,
                PhoneNumber = employeeViewModel.PhoneNumber,
                Address = employeeViewModel.Address,
                EmployeePositions = new List 
                {
                    new EmployeePosition 
                    {
                        PositionId=employeeViewModel.PositionId,
                        EmployeeId=employeeViewModel.EmployeeId
                    }
                }
            };           

            if (employee == null)
                throw new ArgumentNullException("Employee Update");
            _employeeRepository.Update(employee);
            _employeePositionRepository.UpdateCollection(employee.EmployeePositions);
        }

In Repository Class

public void UpdateCollection(ICollection collection)
        {
            if (collection == null)
                throw new ArgumentNullException("collection is null");
            foreach (var item in collection)
            {
                DataContext.Entry(item).State = EntityState.Deleted;
            }
            this.DataContext.SaveChanges();
        }

and COntroller class

[HttpGet]
        public ActionResult Edit(int? id)
        {
            var employee = _employeeService.GetById((int)id);
            if (employee == null) throw new ArgumentNullException("Employee Information Not Found");
            return View(employee);
        }

        [HttpPost]
        public ActionResult Edit(EmployeeViewModel employee)
        {
            _employeeService.Update(employee);
            return RedirectToAction("View", "Employee");
        }

Now when ever update happens I need to delete records in employeeposition table for that employeeid and insert it.
How can I do this