Concise usage of DBNull? (Ternary?)

Question

It seems that there's some type confusion in the ternary operator. I know that this has been addressed in other SO threads, but it's always been with nullables. Also, for my case I'm really just looking for a better way.

I'd like to be able to use

proc.Parameters[PARAM_ID].Value = 
    string.IsNullOrEmpty(dest.Id) ? DBNull.Value : dest.Id;

but instead I'm stuck with this:

if (string.IsNullOrEmpty(dest.Id))
{
    proc.Parameters[PARAM_ID].Value = DBNull.Value;
}
else
{
    proc.Parameters[PARAM_ID].Value = dest.Id;
} 

The ternary operator fails because there's no conversion possible between DBNull and string, and as silly as that seems considering Value is object, the compiler kicks it back to me and I'm forced to care. The answer to the nullable version of this question is to just cast null to string and be done with it; DBNull can't be cast to string, though, so no luck there.

Is there a more concise way to do this (without using nullables, by the way?)

Thanks!

Plow

Answer 1

You could change your first statement to:

proc.Parameters[PARAM_ID].Value = 
    string.IsNullOrEmpty(dest.Id) ? (object)DBNull.Value : dest.Id;

Empire

Oh. Duh. Aaand that's what stackoverflow is for. Thanks! – Plow

Answer 2

Or you could add an extension method such as:

public static class DBNullExtensions
{
    public static object AsDBNullIfEmpty(this string value)
    {
        if (String.IsNullOrEmpty(value))
        {
            return DBNull.Value;
        }
        return value;
    }
}

And then you could just say

proc.Parameters[PARAM_ID].Value = dest.Id.AsDBNullIfEmpty();

(Adapted from Phil Haack)

Readable and concise, no?

Greg

I dig the use of extension methods; sadly this project is on C#2.0 though. Boo hiss. – Plow

Bummer! Maybe you can chisel something out of stone obelisks ;) – Greg

Answer 3

The Value property is of type object, so you should cast to object, not string:

proc.Parameters[PARAM_ID].Value = string.IsNullOrEmpty(dest.Id)
    ? (object)DBNull.Value
    : (object)dest.Id;

Lampyrid

I'm going to give the answer to Jacob since he apparently answered first by about 20 seconds. Thanks to you too mark! – Plow

Answer 4

What about using the ?? null-coalescing operator More details about ?? operator

proc.Parameters[PARAM_ID].Value = dest.Id ?? (object)DBNull.Value;

Schechter

Operator '??' cannot be applied to the type 'bool' and 'object'. If you remove '(object)', compiler will complain about the 'DBNull' type instead of 'object'. – Playa

@Playa the ?? operator can only be used on nullable types, as lhs ?? rhs is essentially equivalent to lhs != null ? lhs : rhs. That is why you are getting "cannot be applied to the type 'bool'" - bool is not nullable! – Ob

@Playa if you want to pass null to the DB its supposed to be a nullable value. the ?? operator con only be used with nullable types. Makes sense, right? – Schechter