Question

这是我的自我参照模型，它是两个连接表：

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

它似乎运行良好......我可以在rails控制台中执行此操作：

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>]>

但是，我需要找出父协会，但无法弄清楚如何做到这一点：

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>

什么都没有用！

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

但是您可能希望将父级的id存储在Discourse模型上，并且可能通过多态（使用STI）拥有Discourse？我觉得如果没有查看关联就能告诉对象的类型是很奇怪的。

通过直通表获取父对象

1 个答案: