find_sti_class

# File activerecord/lib/active_record/inheritance.rb, line 179
      def find_sti_class(type_name)
        if store_full_sti_class
          ActiveSupport::Dependencies.constantize(type_name)
        else
          compute_type(type_name)
        end
      rescue NameError
        raise SubclassNotFound,
          "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " +
          "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " +
          "Please rename this column if you didn't intend it to be used for storing the inheritance class " +
          "or overwrite #{name}.inheritance_column to use another column for that information."
      end