獲取父對象

Question

這是我自己參考模型和它的兩個連接表：

class Discourse < ActiveRecord::Base 
    belongs_to :forum 
    belongs_to :user 

    has_many :impressions 

    has_many :discourse_replies 
    has_many :replies, through: :discourse_replies 

    has_many :reply_retorts 
    has_many :retorts, through: :reply_retorts 
end 

class DiscourseReply < ActiveRecord::Base 
    belongs_to :discourse 
    belongs_to :reply, class_name: 'Discourse', foreign_key: 'reply_id' 
end 

class ReplyRetort < ActiveRecord::Base 
    belongs_to :reply 
    belongs_to :retort, class_name: 'Discourse', foreign_key: 'retort_id' 
end 

這似乎運作良好...我可以在鐵軌控制檯做到這一點：

2.0.0p247 :044 > fd = Discourse.create(title: 'first', body: 'first') 
=> #<Discourse id: 139, user_id: nil, title: "first", body: "first", deleted: nil, delete_date: nil, created_at: "2014-04-07 20:38:06", updated_at: "2014-04-07 20:38:06", forum_id: nil> 

2.0.0p247 :046 > fdr = fd.replies.create(title: 'second relpy to first', body: 'second reply to first')  
=> #<Discourse id: 141, user_id: nil, title: "second relpy to first", body: "second reply to first", deleted: nil, delete_date: nil, created_at: "2014-04-07 20:38:51", updated_at: "2014-04-07 20:38:51", forum_id: nil> 

2.0.0p247 :047 > fdrr = fdr.retorts.create(title: 'a reply to a reply', body: 'a reply to a reply') 
=> #<Discourse id: 142, user_id: nil, title: "a reply to a reply", body: "a reply to a reply", deleted: nil, delete_date: nil, created_at: "2014-04-07 20:39:27", updated_at: "2014-04-07 20:39:27", forum_id: nil> 

2.0.0p247 :048 > fdrrr = fdrr.retorts.create(title: 'a reply to a reply to a reply', body: 'a reply to a reply reply') 
=> #<Discourse id: 143, user_id: nil, title: "a reply to a reply to a reply", body: "a reply to a reply reply", deleted: nil, delete_date: nil, created_at: "2014-04-07 20:39:47", updated_at: "2014-04-07 20:39:47", forum_id: nil> 

2.0.0p247 :050 > fdr.retorts 
=> #<ActiveRecord::Associations::CollectionProxy [#<Discourse id: 142, user_id: nil, title: "a reply to a reply", body: "a reply to a reply", deleted: nil, delete_date: nil, created_at: "2014-04-07 20:39:27", updated_at: "2014-04-07 20:39:27", forum_id: nil>]> 

不過，我需要找出家長協會，但無法弄清楚如何做到這一點：

2.0.0p247 :053 > fdr.discourse # I want this to return the 'fd' instance 
NoMethodError: undefined method `discourse` for #<Discourse:0x00000007080eb0> 

2.0.0p247 :055 > fdrrr.reply # I want this to return the 'fdrr' instance 
NoMethodError: undefined method `reply` for #<Discourse:0x000000070db860> 

2.0.0p247 :055 > fdrrr.parent # I want this to return the 'fdrr' instance 
NoMethodError: undefined method `parent' for #<Discourse:0x0000000672b428> 

2.0.0p247 :055 > fdrrr.parent.try(:id) # I want this to return the 'fdrr' instance 
NoMethodError: undefined method `parent' for #<Discourse:0x0000000672b428> 

沒有什麼工作！

Answer 1

class Discourse < ActiveRecord::Base 
    def reply 
     DiscourseReply.where(reply_id: id).first.try(:discourse) || 
     ReplyRetort.where(retort_id: id).first.try(:reply) 
    end 

    alias_method :parent, :reply 
    alias_method :discourse, :reply 
end 

但你可能要存儲在Discourse模型父的ID，並有可能通過多態（使用STI）Discourse？我覺得如果不查看關聯就不能說出對象的類型，這很奇怪。