Missing Method as Filter

Let's say I have a model called User. User has two attributes or table
columns: id, username

By using the code below I can check that there is a username "Tom" and
return 1 ifthere is and 0 if there is not

User.find_by_username("Tom")? 1 : 0

How would I find out Tom's corresponding id?

For example I'm looking for something along the lines of:
User.find_by_username("Tom").id

That will work except that you should probably check that Tom exists,
as it will throw an error if he does not (as you would be effectively
saying nil.id).

Colin

(user = User.find_by_username("Tom")) ? user.id : 0