rails 1.99.0

app/model/child.rb
class Child < ActiveRecord::Base
validates_length_of :name, :minimum => 5 #Childは5文字
end

app/model/child_a.rb
class ChildA < Child
validates_length_of :name, :minimum => 3 #ChildAは3文字でOK
end

script/console
>> ChildA.new(:name => 'XXX').valid? #3文字ならOKのはずだが、
#=> false
>> ChildA.new(:name => 'XXXXX').valid? # 5文字は問題なし
#=> true

なるほど。

>> c = ChildA.new(:name => 'X'); c.valid?; c.errors.map(&:to_s)
=> ["nameis too short (minimum is 5 characters)", "nameis too short (minimum is 3 characters)"]

ChildAのvalidationも呼ばれてはいるようですね。