is
Jon Skeet
A little bit of string cast
Update:
When a database returns a value through the scalar, it will always be an object. So when the value is returned you should have a preconceived notion of what the type will be. Why would you use ToString(); when you you have a SELECT which passes two parameters.
As if it doesn't exist it will always throw a null. So in my refactor I believed the as would be the proper approach. As ToString() will throw an error --- So what form of cast is it comparable to?
I've got some code I'm maintaining, but in apart of my refactor I came across a ToString() attached to an ExecuteScalar. My question would be, does the usage of ToString() equate to:
(string)command.ExecuteScalar();
Or would it represent this:
command.ExecuteScalar() as string;
Obviously the as string would fail gracefully, where the cast (string) would actually fall into an InvalidCastException. So when you call:
command.ExecuteScalar().ToString();
Which method of casting is it attempting to do?
No, it doesn't mean either of those - it simply means calling ToString() on whatever the value is.
In particular, if the value is not a string, it will convert it to a string anyway - whereas string would fail with InvalidCastException and the as would return null.
So for example:
object x = 10;
string a = x.ToString(); // "10"
string b = x as string; // null
string c = (string) x; // Bang
Of course, ToString() can still throw an exception too - most obviously if the target of the call is a null reference.
Personally, I would suggest using a cast if you know what the result type should be - although the result of ExecuteScalar is more commonly a numeric value (e.g. a count) rather than a string.
Yes, that means an exception will be thrown if you're wrong - but if your query isn't doing what it's meant to anyway, then stopping due to an exception may well be better than going ahead with a bogus view of the world. (See my blog post on casting vs as for more on this attitude.)
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