新手问题 模型中 type 字段的魔法 ？？？
class A < ActiveRecord::Base
attr_accssor :type ...
end
class B < A
end
class C < A
end
a = A.new
b = B.new
c = C.new
puts a.type #=> nil
puts b.type #=> B
puts c.type #=> C
b 和 c 中的 type 字段 自动获取值为 所属类名。求问这类的情况是可以在哪里查到具体说明？
type 是 active_record 的保留字段
Single table inheritance
Active Record allows inheritance by storing the name of the class in a column that by default is named “type” (can be changed by overwriting Base.inheritance_column). This means that an inheritance looking like this:
