Rails協會 - has_many =>：通過 - 但相同的型號

Question

我在做什麼：

我有一個博客，並希望顯示主帖子下面的相關帖子。

class Post < ActiveRecord::Base 

    has_many :related_posts 
    has_many :posts, :through => :related_posts 

end 

然後在過程中的連接模型/表

class RelatedPost < ActiveRecord::Base 

    belongs_to :post 

end 

而且還有一個表中調用related_posts有兩個post_id列。

很明顯，這有幾個缺陷，我只是不知道如何使這種關聯在Rails中工作。

Answer 1

這是一個有趣的問題。

我剛剛爲您的用例創建了一個工作應用程序。

post.related_posts會給你所有帖子相關的帖子，而post.inverse_related_posts會給你所有帖子相關的帖子。

這裏是我的模型是這樣的：

class Post < ActiveRecord::Base 
    has_many :related_posts_association, :class_name => "RelatedPost" 
    has_many :related_posts, :through => :related_posts_association, :source => :related_post 
    has_many :inverse_related_posts_association, :class_name => "RelatedPost", :foreign_key => "related_post_id" 
    has_many :inverse_related_posts, :through => :inverse_related_posts_association, :source => :post 
end 

class RelatedPost < ActiveRecord::Base 
    belongs_to :post 
    belongs_to :related_post, :class_name => "Post" 
end 

我的架構：

ActiveRecord::Schema.define(:version => 20110702194300) do 

    create_table "posts", :force => true do |t| 
    t.string "name" 
    t.datetime "created_at" 
    t.datetime "updated_at" 
    end 

    create_table "related_posts", :force => true do |t| 
    t.integer "post_id" 
    t.integer "related_post_id" 
    t.datetime "created_at" 
    t.datetime "updated_at" 
    end 

end 

這裏有一個控制檯會話的是展示了關係轉儲。

ruby-1.9.2-p180:001:0>> p = Post.create! name: "Hello" 
    SQL (23.5ms) INSERT INTO "posts" ("created_at", "name", "updated_at") VALUES (?, ?, ?) [["created_at", Sat, 02 Jul 2011 20:03:43 UTC +00:00], ["name", "Hello"], ["updated_at", Sat, 02 Jul 2011 20:03:43 UTC +00:00]] 
# => #<Post id: 1, name: "Hello", created_at: "2011-07-02 20:03:43", updated_at: "2011-07-02 20:03:43"> 
ruby-1.9.2-p180:002:0>> p2 = Post.create! name: "World" 
    SQL (1.0ms) INSERT INTO "posts" ("created_at", "name", "updated_at") VALUES (?, ?, ?) [["created_at", Sat, 02 Jul 2011 20:03:48 UTC +00:00], ["name", "World"], ["updated_at", Sat, 02 Jul 2011 20:03:48 UTC +00:00]] 
# => #<Post id: 2, name: "World", created_at: "2011-07-02 20:03:48", updated_at: "2011-07-02 20:03:48"> 
ruby-1.9.2-p180:003:0>> p.related_posts 
    Post Load (0.2ms) SELECT "posts".* FROM "posts" INNER JOIN "related_posts" ON "posts"."id" = "related_posts"."related_post_id" WHERE "related_posts"."post_id" = 1 
# => [] 
ruby-1.9.2-p180:004:0>> p2.related_posts 
    Post Load (0.4ms) SELECT "posts".* FROM "posts" INNER JOIN "related_posts" ON "posts"."id" = "related_posts"."related_post_id" WHERE "related_posts"."post_id" = 2 
# => [] 
ruby-1.9.2-p180:005:0>> p.related_posts << p2 
    SQL (0.7ms) INSERT INTO "related_posts" ("created_at", "post_id", "related_post_id", "updated_at") VALUES (?, ?, ?, ?) [["created_at", Sat, 02 Jul 2011 20:04:01 UTC +00:00], ["post_id", 1], ["related_post_id", 2], ["updated_at", Sat, 02 Jul 2011 20:04:01 UTC +00:00]] 
# => [#<Post id: 2, name: "World", created_at: "2011-07-02 20:03:48", updated_at: "2011-07-02 20:03:48">] 
ruby-1.9.2-p180:006:0>> RelatedPost.all 
    RelatedPost Load (0.4ms) SELECT "related_posts".* FROM "related_posts" 
# => [#<RelatedPost id: 1, post_id: 1, related_post_id: 2, created_at: "2011-07-02 20:04:01", updated_at: "2011-07-02 20:04:01">] 
ruby-1.9.2-p180:007:0>> p2.inverse_related_posts 
    Post Load (0.2ms) SELECT "posts".* FROM "posts" INNER JOIN "related_posts" ON "posts"."id" = "related_posts"."post_id" WHERE "related_posts"."related_post_id" = 2 
# => [#<Post id: 1, name: "Hello", created_at: "2011-07-02 20:03:43", updated_at: "2011-07-02 20:03:43">] 
ruby-1.9.2-p180:008:0>> p = Post.first 
    Post Load (0.5ms) SELECT "posts".* FROM "posts" LIMIT 1 
# => #<Post id: 1, name: "Hello", created_at: "2011-07-02 20:03:43", updated_at: "2011-07-02 20:03:43"> 
ruby-1.9.2-p180:009:0>> p2.related_posts << p 
    SQL (25.7ms) INSERT INTO "related_posts" ("created_at", "post_id", "related_post_id", "updated_at") VALUES (?, ?, ?, ?) [["created_at", Sat, 02 Jul 2011 20:05:29 UTC +00:00], ["post_id", 2], ["related_post_id", 1], ["updated_at", Sat, 02 Jul 2011 20:05:29 UTC +00:00]] 
    Post Load (0.3ms) SELECT "posts".* FROM "posts" INNER JOIN "related_posts" ON "posts"."id" = "related_posts"."related_post_id" WHERE "related_posts"."post_id" = 2 
# => [#<Post id: 1, name: "Hello", created_at: "2011-07-02 20:03:43", updated_at: "2011-07-02 20:03:43">] 
ruby-1.9.2-p180:010:0>> p2.related_posts 
# => [#<Post id: 1, name: "Hello", created_at: "2011-07-02 20:03:43", updated_at: "2011-07-02 20:03:43">] 
ruby-1.9.2-p180:011:0>> exit 


Loading development environment (Rails 3.1.0.rc4) 
ruby-1.9.2-p180:001:0>> Post.first.related_posts 
    Post Load (0.3ms) SELECT "posts".* FROM "posts" LIMIT 1 
    Post Load (0.2ms) SELECT "posts".* FROM "posts" INNER JOIN "related_posts" ON "posts"."id" = "related_posts"."related_post_id" WHERE "related_posts"."post_id" = 1 
# => [#<Post id: 2, name: "World", created_at: "2011-07-02 20:03:48", updated_at: "2011-07-02 20:03:48">] 
ruby-1.9.2-p180:002:0>> Post.last.related_posts 
    Post Load (0.2ms) SELECT "posts".* FROM "posts" ORDER BY "posts"."id" DESC LIMIT 1 
    Post Load (0.2ms) SELECT "posts".* FROM "posts" INNER JOIN "related_posts" ON "posts"."id" = "related_posts"."related_post_id" WHERE "related_posts"."post_id" = 2 
# => [#<Post id: 1, name: "Hello", created_at: "2011-07-02 20:03:43", updated_at: "2011-07-02 20:03:43">] 

Answer 2

您正在尋找自我指涉關聯。

我建議你把靈感here.