Is it possible to coalesce string and DBNull in C#?

Question

I\'m writing a C# routine to call a stored proc. In the parameter list I\'m passing in, it is possible that one of the values can legally be null. So I thought I\'d use a

Answer 1

new SqlParameter("@theParam", (object)theParam ?? DBNull.Value)

Answer 2

The reason you can't use the null coalesce operator is that it has to return one type and you are providing more than one type. theParam is a string. DbNull.Value is a reference to a static instance of type System.DbNull. This is what its implementation looks like;

public static readonly DBNull Value = new DBNull(); 
//the instantiation is actually in the 
//static constructor but that isn't important for this example

So if you were to have a NullCoalesce method, what would its return type be? It can't be both System.String and System.DbNull, it has to be one or the other, or a common parent type.

So that leads to this type of code;

cmd.Parameters.Add(
    new SqlParameter("@theParam", (object)theParam ?? (object)DBNull.Value)
);

Answer 3

I'm pretty sure that just passing a null to the SqlParameter constructor results in it being sent as a DBNull.Value... I may be mistaken, since I use the EnterpriseLibraries for DB access, but I'm quite sure that sending a null is fine there.

Answer 4

Use this syntax:

(theParam as object) ?? (DBNull.Value as object)

In this case both parts of operator ?? are of the same type.