Same variable name in different class but one is nullable

Question

I have the following classes which have the same variable, but one of them is nullable, the other one is not because it is a primary key in that table:

[DataServiceKey("OrderID")]
public class Order
{
    public int OrderID { get; set; }
    public int? EmployeeID { get; set; }
    // ...other properties...
    // ...

    public Employee Employees { get; set; }
}

[DataServiceKey("EmployeeID")]
public class Employee
{
    public int EmployeeID { get; set; }
    // ...other properties...
    // ...

    public IEnumerable<Order> Orders { get; set; }
}

The general idea between these 2 classes is an order can belong to 1 Employee, but there might also exist an order that is not assigned to any Employee yet, an Employee must have at least 1 order or more than 1. Now I am trying to create an association between Order class and Employee class, and this is how I did:

        // Create an association between Orders and Employees
        var _es = _Employees.ToDictionary(e => e.EmployeeID);
        var _os = _Orders.ToLookup(o => o.EmployeeID);
        foreach (var o in _Orders) o.Employees = _es[o.EmployeeID];
        foreach (var e in _Employees) e.Orders = _os[e.EmployeeID];

I got cannot convert from "int?" to "int" error in _es[o.EmployeeID], I have tried every solutions provided in here, but none of them are work for me...I have also tried to use _es[o.EmployeeID.Value], it does solve the error but this time it gaves me System.InvalidOperationException error when I run it. Is there any possible solution will be applied to my issue ?

you can try like this `foreach (var o in _Orders) o.Employees = _es[o.EmployeeID] ?? Default(int);` — Krsna Kishore, Sep 09 '16 at 05:02

score 3 · Accepted Answer · answered Sep 09 '16 at 05:00

3

You're passing an int? for a key to a dictionary where int is needed.

o.Employee is an int?.

es is a Dictionary<int, Employee>.

You probably want:

o.Employees = o.EmployeeID != null ? _es[o.EmployeeID] : null;

answered Sep 09 '16 at 05:00

Cory Nelson

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Instead of checking `null`, check whether it has value using `HasValue` – Balagurunathan Marimuthu Sep 09 '16 at 05:03
@BalagurunathanMarimuthu checking for `null` is the way most idiomatic to C#. It is syntax sugar for `HasValue` -- the two are identical. – Cory Nelson Sep 09 '16 at 05:07
Yes, I agree.. but `Nullable` variable contains predefined property to check whether the variable has value or null. – Balagurunathan Marimuthu Sep 09 '16 at 05:09

score 1 · Answer 2 · answered Sep 09 '16 at 05:00

Check HasValue before assign the value.

foreach (var o in _Orders)
{
    if (_es[o.EmployeeID].HasValue)
    {
        o.Employees = _es[o.EmployeeID];
    }
}

or

foreach (var o in _Orders) o.Employees = _es[o.EmployeeID].HasValue ? _es[o.EmployeeID] : null;

Same variable name in different class but one is nullable

2 Answers2