find() with nil when there are no records
Solution 1:
Yes, just do:
Challenge.find_by_id(10)
For Rails 4 and 5:
Challenge.find_by(id: 10)
Solution 2:
In Rails 4, dynamic finders - such as find_by_id which was used in the accepted answer - were deprecated.
Moving forward, you should use the new syntax:
Challenge.find_by id: 10
Solution 3:
you can do this a bit hackish, just use the ActiveRecord Query Interface.
this will return nil, instead of raising a Exception
User.where(:id => 10).first