instance method find_sti_class

# File activerecord/lib/active_record/inheritance.rb, line 132
      def find_sti_class(type_name)
        if type_name.blank? || !columns_hash.include?(inheritance_column)
          self
        else
          begin
            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
        end
      end