ASP.NET VB - Conversion from type 'DBNull' to type 'String' is not valid

Question

I have the following ASP.NET (VB) code:

    strLocation = CStr(q1("LocationName")) + " " + CStr(q1("LocationAddress")) + " " + CStr(q1("LocationCity"))

As LocationCity is null:

I get Conversion from type 'DBNull' to type 'String' is not valid.

Is there a way to fix this.

If it was only LocationCity I would probably do something like:

    If IsDBNull(q1("LocationCity")) Then
        strLocation = ""
    Else
        strLocation = CStr(q1("LocationCity"))
    End If

I also tried:

    strLocation = If(CStr(q1("LocationName")), "") + " " + If(CStr(q1("LocationAddress")), "") + " " + If(CStr(q1("LocationCity")), "")

but got the same result

In C# I would normally use ?? but not sure of the best approach in ASP.NET VB

Answer 1

The equivalent to the C# ?? in VB.NET is the IF Operator

strLocation = If(IsDBNull(q1("LocationCity")), "", CStr(q1("LocationCity")))

Do not use the IIF Function as it is deprecated, doesn't support short circuiting and is not type safe.

Also see Is there a VB.NET equivalent for C#'s ?? operator? for related information

Answer 2

You could use If(IsDBNull(q1("propertyName")), "", CStr(q1("propertyName")))

Or you could implement the code block you showed as a method and call that method for each property. IMO, it would make your line of code much cleaner than using 3 IIF statements

Function StringValue(q1 as Q1Type) as String
    If IsDBNull(q1("LocationCity")) Then   
        Return ""   
    Else   
        Return  CStr(q1("LocationCity"))   
    End If
End Function

strLocation = StringValue(q1("LocationName")) + " " + StringValue(q1("LocationAddress")) + " " + StringValue(q1("LocationCity"))