The String#constantize method is a feature that makes rails fun to code with. This method converts a string to the constant that the string contains (or throws a NameError if there is no such constant). It makes it easy to store class-types in databases as strings and to code controllers that work with classes of the same duck type. Most people know that eval on user data is dangerous, but noboddy seems to care about constantize. Beware, it is also dangerous and you should constantize with care!