Nsryjdtyk

Basically I am decouple my code by introducing an Employee Repository to handle all the database interaction. My problem is that my code performs instruction but then throws

System.InvalidOperationException: 'Sequence contains no elements'.

I have tried using FirstOrDefault and SingelOrDefault as suggested but previous posts I've read but it performs the remove operation and throws

System.NullReferenceException: 'Object reference not set to an
instance of an object.'

removeEmployee was null. Can someone help explain to me how to fix it

This is the code I am trying to refactor and this initial code worked without throwing an exception:

[HttpPost]

public IActionResult Remove(int employeeIds)

{ 



    foreach (int employeeId in employeeIds)

    {

        Employee removeEmployee = context.Employees.Single(c => c.EmployeeID == employeeId);



        if (removeEmployee.WorkStatus == "Available")

        {

           context.Employee.Remove(removeEmployee);

        }

        else

        {

           return Redirect("/Employee/Remove");

        }



   }

   context.SaveChanges();

   return Redirect("/");

}

Below is how I am trying to refactor my code.

Employee Repoistory:

 public bool RemoveEmployee(int employeeIds)

    {

        foreach (int employeeId in employeeIds)

        {

            Employee removeEmployee = context.Employees.Single(c => c.EmployeeID == employeeId);



            if (removeEmployee.WorkStatus == "Available")

            {

                context.Employees.Remove(removeEmployee);

            }

            else

            {

                return false;

            }

        }

        context.SaveChanges();

        return true;

    }

Employee Controller:

private IEmployeesRepository repo;



    public EmployeeController(IEmployeesRepository repo)

    {

        this.repo = repo;

    }



 [HttpPost]

    public IActionResult Remove(int employeeIds)

    {

        repo.RemoveEmployee(employeeIds);



        if (repo.RemoveEmployee(employeeIds) == false)

        {

            return Redirect("/Employee/Remove");

        }

        else

        {

            return Redirect("/");

        }

    }

As Ross Bush pointed out, the line of code mentioned by JohnB throws invalid operation exception if the predicate (c => c.EmployeeID == employeeId) yields 0 results when your method is just 'Single'. If you put 'SingleOrDefault' the result will be null. So "removeEmployee" will be null. When you access any member under removeEmployee which is now null (like "removeEmployee.WorkStatus"), it will throw the null reference exception.

I am not sure how your code worked before. Your first version of code has context.Employee, but your modified version has context.Employees. I suspect there is something going on there or it might be that when you tested with the original code, there might have been some data

Thanks to everybody that bothered to look at my problem and tried to help me find a solution. The problem with my code actually had to do with the logic in my "RemoveEmployee" Method and the return Boolean value. Below is the solution I came up with.

Employee Repository:

public bool RemoveEmployee(int employeeIds)

        {

            foreach (int employeeId in employeeIds)

            {

                Employee removeEmployee = context.Employees.Single(c => c.EmployeeID == employeeId); 

                if (removeEmployee !=null && removeEmployee.WorkStatus == "Available")

                {

                    context.Employees.Remove(removeEmployee);

                    context.SaveChanges();

                    return true;

                }        

            }

            return false;

        }

Employeee Controller:

[HttpPost]

        public IActionResult Remove(int employeeIds)

        {                   

            if (repo.RemoveEmployee(employeeIds) == false)

            {

                return Redirect("/Employee/Remove");

            }

            else

            {

                return Redirect("/Employee");

            }

        }