Rails关联 – has_many =>：通过 – 但是相同的模型
我在做什么：
我有一个博客，并希望显示主帖下面的相关post。
class Post < ActiveRecord::Base has_many :related_posts has_many :posts, :through => :related_posts end 然后在连接模型/表中
class RelatedPost < ActiveRecord::Base belongs_to :post end
当然，还有一个名为related_posts的表格，带有两个post_id列。
显然这里有一些缺陷，我只是不知道如何使这种关联在Rails中工作。
这是一个有趣的问题。
我刚刚为您的用例创build了一个可用的应用程序。
post.related_posts会给你所有post相关的职位，而post.inverse_related_posts会给你所有职位相关的职位。
以下是我的模型的样子：
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
我的模式：
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
这是一个控制台会话的转储，展示了这种关系。
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">]
你正在寻找自我指涉关系。
我build议你在这里获得灵感。
