有没有办法检查Rails 3.1中是否存在has_many关联？

Question

例如,有一些模型

class Model_1 < ActiveRecord::Base
   has_many :images, :as => :imageable
end

class Model_2 < ActiveRecord::Base
   # doesn't have has_many association
end
...
class Image < ActiveRecord::Base
    belongs_to :imageable, :polymorphic => true
end

如何检查该模型是否具有has_many关联？像这样的东西

class ActiveRecord::Base
    def self.has_many_association_exists?(:association)
        ...
    end
end

它可以这样使用

Model_1.has_many_association_exists?(:images) # true
Model_2.has_many_association_exists?(:images) # false

提前致谢

Answer 1

怎么样reflect_on_association？

Model_1.reflect_on_association(:images)

或者reflect_on_all_associations:

associations = Model_1.reflect_on_all_associations(:has_many)
associations.any? { |a| a.name == :images }