Problem inserting string or NULL into SQL Server database

Question

I just read the top answer at this post:
Problem inserting string or NULL into SQL Server database

Correct me if I'm wrong, but can the ??-operator not only be used on two variables of the same type, if not I would greatly appreciate it, if anyone could solve my minor problem.

I tried to insert some code in my project similar to the one below.

Dictionary<string, string> strings = new Dictionary<string, string>()
{
    {"@param0", strParam0},
    {"@param1", strParam1},
    {"@param2", strParam2}
};
foreach (string param in strings.Keys)
{
    cmd.Parameters.AddWithValue(param, strings[param] ?? DBNull.Value);
}

But Visual Studio complains with the following message:
"Operator '??' cannot be applied to operands of type 'string' and 'System.DBNull'"

Mehrdad Afshari · Accepted Answer · 2009-02-27 10:09:43Z

4

Try:

cmd.Parameters.AddWithValue(param, (object)strings[param] ?? DBNull.Value);

answered Feb 27, 2009 at 10:09

Mehrdad Afshari

424k93 gold badges864 silver badges796 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Erik Funkenbusch · Accepted Answer · 2009-02-27 10:21:58Z

0

DBNull and Null are not the same type, nor are nullable types or reference types and DBNull. You can only use ?? with values of the same type.

One can think of the ?? operator as syntactic sugar for:

(left != null) ? left : right

And the ternary operation requires both left and right to be of the same type, so therefore left and right of the ?? operator must also be of the same type.

So, unfortunately, no.. you can't do it this way, at least not without some ugly casting.

edited Feb 27, 2009 at 10:21

answered Feb 27, 2009 at 10:08

Erik Funkenbusch

93.6k29 gold badges201 silver badges292 bronze badges

Comments

Neil Bostrom · Accepted Answer · 2009-02-27 10:18:51Z

0

    cmd.Parameters.AddWithValue(param, strings[param] == null ? DBNull.Value : strings[param]);

Only flaw is that it will do the dictionary look up twice!

answered Feb 27, 2009 at 10:18

Neil Bostrom

2,35921 silver badges27 bronze badges

2 Comments

LukeH Over a year ago

There's another flaw - it won't compile! You can't convert directly from string to DBNull, regardless of whether you use ?? or ?: for this.

Neil Bostrom Over a year ago

* tries it * You are right... It needs the trick above (object)DBNull.Value

Collectives™ on Stack Overflow

Problem inserting string or NULL into SQL Server database

3 Answers 3

Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related