Question

I have a null value in my database which gives me an error if I try perform any mathematical operations on it. I tried putting this in my controller action:

If String.IsNullOrEmpty(item.Tbl_Food.Fiber_TD_g) Then
            item.Tbl_Food.Fiber_TD_g = 0
End If

This my model for the field:

Public Property Fiber_TD_g() As Nullable(Of Double)

However, it says “Nullable object must have a value.” on the If String.IsNullOrEmpty(item.Tbl_Food.Fiber_TD_g) Then line. How can I check if the “string” (it’s a double, not a string) is empty and default it to zero, properly?

Edit:

I tried a suggestion below, and I no longer get an error in my controller, but instead in my View. It says, “Nullable object must have a value.” on the line FiberTotal += item.Tbl_Food.Fiber_TD_g in my view.

Dim food = db.Tbl_Food_Logs.Where(Function(x) x.FLog_Employee_ID = empId And x.FLog_Created_Date >= date2 And x.FLog_Created_Date < tomorrow)

For Each item In food

    If IsDBNull(item.Tbl_Food.Fiber_TD_g) Then
        item.Tbl_Food.Fiber_TD_g = 0
    End If

Next
Return View(food)

Answer 1

As its name implies, String.IsNullOrEmpty is a string operation. It won’t work if you pass a double. Instead check to see if it Is Nothing:

If item.Tbl_Food.Fiber_TD_g Is Nothing Then
            item.Tbl_Food.Fiber_TD_g = 0
End If

This operation is common enough that VB has a shortcut, called the null coalescing operator (2-argument If):

item.Tbl_Food.Fiber_TD_g = If(item.Tbl_Food.Fiber_TD_g, 0)

When If has two arguments, it returns the first argument if it’s not null and the second if it is.