Question

I have written some LINQ where I check against a database whether or not the username is unique when I am adding a new user. My code (see below) works, but is there a better way to do this? I am currently relying on trapping an error if the username does not exist.

try
        {
            var User = (from u in _database.Users
                        where u.UserID == strUserName
                        select u).First();

            if (User != null)
            {
                blnUnique = false;
            }
        }
        catch
        {
            blnUnique = false;
        }

Answer 1

You can use the Enumerable.Any<TSource>() extension method:

bool isUnique = (from u in database.Users
                 where u.UserID == userName
                 select u).Any();

Here’s an alternative way of expressing this using a lambda:

bool isUnique = database.Users.Any(u => u.UserID == userName);

Note that the equals operator on the String class will make a case-sensitive ordinal comparison. If you wish to make a case-insensitive comparison you’ll have to use the String.Equals method:

bool isUnique = database.Users.Any(
    u => u.UserID.Equals(userName, StringComparison.OrdinalIgnoreCase));