Exception When Casting String Object to SqlString

Question

I have a simple cast issue in following simple c# method

using System;
using System.Data.SqlTypes;

...

private void method1() {
    string s = "TestString";
    object o = s;
    SqlString t1 = (SqlString) s;
    SqlString t2 = (SqlString) o;
}

...

When casting directly from s (in case of t1), I don't get any error but when casting from o I get exception:

Specified cast is not valid.

I have same problem converting from object to all types System.Data.SqlTypes

How can I cast an object that has string in it to SqlString?

Answer 1

This is because there is an implicit conversion operator for String to SqlString.

In other words, you are not dealing with a simple built-in cast: designers of SqlString decided to allow you cast strings to SqlString. They didn't do it for Object, hence the error that you are seeing.

Answer 2

To answer your question

private void method1() {
    object o = "MyString";
    SqlString t1 = o as String        
}

if o is not a string, t1 will be null.

Answer 3

Neither of the other answers addresses the question of casting the object reference to the SqlString. If you are certain that the object reference points to a string, it's simple:

var ss = (SqlString)(string)o;

If o might hold a value other than a string, you can do this, instead:

var ss = (SqlString)(o as string);

Or, if you want to go down the (dangerous) path of storing non-string data in string format:

var ss = o == null ? (SqlString)null : o.ToString();