ruby-on-rails - rails : Including a Concern with a constant within a Concern

Question

我担心存储常量的位置:

module Group::Constants
  extend ActiveSupport::Concern

  MEMBERSHIP_STATUSES = %w(accepted invited requested
    rejected_by_group rejected_group)
end

我希望使用这些常量的另一个问题是:

module User::Groupable
  extend ActiveSupport::Concern
  include Group::Constants

  MEMBERSHIP_STATUSES.each do |status_name|
    define_method "#{status_name}_groups" do
      groups.where(:user_memberships => {:status => status_name})
    end
  end
end

不幸的是，这会导致路由错误:

uninitialized constant User::Groupable::MEMBERSHIP_STATUSES

看起来第一个问题在第二个问题中没有正确加载。如果是这样，我该怎么办？

Answer 1

看来这种行为是设计使然，正如 here 中所解释的那样.

在这种情况下，您需要做的不是 Group::Constants延伸自 ActiveSupport::Concern因为这将阻止其实现与其他 ActiveSupport::Concern 共享扩展模块(尽管最终将在包含第二个模块的类中共享):

module A
  TEST_A = 'foo'
end

module B
  extend ActiveSupport::Concern
  TEST_B = 'bar'
end

module C
  extend ActiveSupport::Concern
  include A
  include B
end

C::TEST_A 
=> 'foo'
C::TEST_B 
=> uninitialized constant C::TEST_B

class D
  include C
end

D::TEST_A 
=> 'foo'
D::TEST_B 
=> 'bar'

简而言之，您需要制作 Group::Constants一个标准模块，然后一切都会好起来的。