validations of "type" when using Single Table Inheritance

Sorry if I'm just dumbing out, but is there a reason that when using
Single Table Inheritance Rails doesn't really validate the "type"
field or provide some mechanism to do so? seems like a good way to
corrupt a database. Because the "type" is also a special attribute, I
had to resort to an ugly hack like:

  class ActiveRecord::Base
    def type_attr
      self[:type]
    end
    def self.validates_type(options={})
      validates_inclusion_of :type_attr, options
    end
  end

so that I could write:

  class Fruit < ActiveRecord::Base

    validates_type :allow_nil => true,
                            :in => %w{ Apple } # could be dynamic
subclass_of but make faster!

(obviously this could also have been put on the derived class)

Thanks!

Yes, although it could be changed manually (unlikely) or injected from
cgi parameters, which is what the validations are supposed to prevent,
no?