find_sti_class

# File activerecord/lib/active_record/base.rb, line 979
        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