ActiveRecord STI:如何突破父类的默认范围

Question

在Rails 3.1 RC6上,给出

class Animal < ActiveRecord::Base
  default_scope where(legs: 4)
end

以下内容无法按预期工作:

class Man < Animal
  default_scope unscoped.where(legs: 2)
end

生成的SQL语句如下所示:

SELECT * FROM animals WHERE legs = 4 AND legs = 2

如何完全覆盖父类的默认范围？

我也尝试了以下所有工作:

default_scope{ unscoped.where legs: 2 }
default_scope with_exclusive_scope{ legs: 2 }

Answer 1

我挖掘了Rails的源代码,并提出了一个在Rails 3.1下运行的解决方案(使用activerecord 3.1.0.rc6测试):

class Animal < ActiveRecord::Base
  default_scope where(legs: 4)
end

class Man < Animal
  self.default_scopes = []
  default_scope where(legs: 2)
end