This article was migrated from http://rails.office.drecom.jp/takiuchi/archive/147

西さん（a.k.a. maiha）のRuby on Rails入門のp112に書かれてる偽STIが面白そうだったので、 instantiateのソースコードをメモ。

# File src/rails-1.1.6/activerecord/lib/active_record/base.rb, line 975
def instantiate(record)
  object = 
    if subclass_name = record[inheritance_column]
      if subclass_name.empty?
        allocate
      else
        require_association_class(subclass_name)
        begin
          compute_type(subclass_name).allocate
        rescue NameError
          raise SubclassNotFound,
            "The single-table inheritance mechanism failed to locate the subclass: '#{ record[inheritance_column] }'. " +
            "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 #{ self.to_s }.inheritance_column to use another column for that information."
        end
      end
    else
      allocate
    end

  object.instance_variable_set("@attributes", record)
  object
end

This article was migrated from http://rails.office.drecom.jp/takiuchi/archive/147