我有一个非常奇怪的问题。
场景：我正在使用MongoDB（mongoid gem）处理Rails中的照片集合，其中每张照片都属于一张相册。一些mongo字段由关注点提供，模型正确命名空间。 所以，
关注：MediaConcerns::Base
module MediaConcerns
module Base
extend ActiveSupport::Concern
included do
field :photo_description, type: String
end
end
end
关注：MediaCollectionConcerns::Base
module MediaCollectionConcerns
module Base
extend ActiveSupport::Concern
included do
field :album_title, type: String
field :album_description, type: String
end
end
end
MediaType::Photo是：
module MediaType
class Photo
include Mongoid::Document
include Mongoid::Timestamps::Short
include MediaConcerns::Base
embedded_in :photo_album, class_name: 'MediaCollection::PhotoAlbum'
end
end
虽然MediaCollection::PhotoAlbum是：
module MediaCollection
class PhotoAlbum
include Mongoid::Document
include Mongoid::Timestamps::Short
include MediaCollectionConcerns::Base
embeds_many :photos, class_name: 'MediaType::Photo'
end
end
是否有问题，问题仍然存在，并且与embedded_in和embeds_many有关。
通过Rails控制台，当我尝试MediaCollection::PhotoAlbum.new时，它会给出：
NoMethodError: private method `existence_check' called for MediaCollection::PhotoAlbum:Class
from /home/marco/.rvm/gems/ruby-2.4.0/gems/mongoid-6.1.0/lib/mongoid/relations/macros.rb:355:in `relate'
from /home/marco/.rvm/gems/ruby-2.4.0/gems/mongoid-6.1.0/lib/mongoid/relations/macros.rb:85:in `embeds_many'
from /home/marco/workspace/backend/app/models/media_collection/photo_album.rb:10:in `<class:PhotoAlbum>'
from /home/marco/workspace/backend/app/models/media_collection/photo_album.rb:2:in `<module:MediaCollection>'
from /home/marco/workspace/backend/app/models/media_collection/photo_album.rb:1:in `<top (required)>'
同样适用于MediaType::Photo.new：
NoMethodError: private method `existence_check' called for MediaType::Photo:Class
from /home/marco/.rvm/gems/ruby-2.4.0/gems/mongoid-6.1.0/lib/mongoid/relations/macros.rb:355:in `relate'
from /home/marco/.rvm/gems/ruby-2.4.0/gems/mongoid-6.1.0/lib/mongoid/relations/macros.rb:56:in `embedded_in'
from /home/marco/workspace/backend/app/models/media_type/photo.rb:15:in `<class:Photo>'
from /home/marco/workspace/backend/app/models/media_type/photo.rb:2:in `<module:MediaType>'
from /home/marco/workspace/backend/app/models/media_type/photo.rb:1:in `<top (required)>'
有什么问题？如果我删除（仅用于调试）关系embeds_many和embedded_in，问题就解决了，但我需要嵌入这些文档！
也许Rails找不到:photos，但我已经指定class_name: 'MediaType::Photo'作为mongoid文档建议，同样指定'MediaCollection::PhotoAlbum'
我需要帮助。感谢。