Rails：使用has_and_belongs_to_many的自联接方案？

I would like to create a structure of Users having many friends, also of class User:

我想创建一个拥有很多朋友的用户结构，也是类User：

class User < ActiveRecord::Base
  has_and_belongs_to_many :friends, class_name: "User"
end

I do not need any details of their relationship thus I do not use :through with kind of class Friendship. But now I cannot find any way how to create corresponding database (neither with migration file nor using rails g model User username:string ... command). Any ideas?

我不需要他们关系的任何细节因此我不使用：通过类友谊。但是现在我找不到任何方法来创建相应的数据库（既不使用迁移文件也不使用rails g model User username：string ...命令）。有任何想法吗？

1 个解决方案

#1

Here are some resources which may be helpful:

以下是一些可能有用的资源：

RailsCasts episode #163 Self-Referential Association regarding self-referential many-to-many relationships
RailsCasts第163集关于自我指涉多对多关系的自我指涉协会
RailsCasts episode #47 Two Many-to-Many. This might be more relevant to what you're attempting to accomplish
RailsCasts第47集两个多对多。这可能与您尝试完成的内容更为相关
A gist someone created for self-referential relationships using HABTM
使用HABTM为自我指涉关系创建的要点

I'll summarize the information found in those links:

我将总结这些链接中的信息：

Given that you're describing a self-referential many-to-many relationship, you will of course end up with a join table. Normally, the join table should be deliberately named in such a way that Rails will automatically figure out which models the table is joining, however the "self-referential" part makes this a tad awkward, but not difficult. You'll merely have to specify the name of the join table, as well as the joining columns.

鉴于您正在描述自引用的多对多关系，您当然最终会得到一个连接表。通常情况下，连接表应该以这样的方式故意命名，即Rails会自动确定表加入的模型，但是“自引用”部分使这有点尴尬，但并不困难。您只需指定连接表的名称以及连接列。

You'll need to create this table using a migration that will probably look something like this:

您需要使用可能如下所示的迁移创建此表：

class CreateFriendships < ActiveRecord::Migration
  def self.up
    create_table :friendships, id: false do |t|
      t.integer :user_id
      t.integer :friend_user_id
    end

    add_index(:friendships, [:user_id, :friend_user_id], :unique => true)
    add_index(:friendships, [:friend_user_id, :user_id], :unique => true)
  end

  def self.down
      remove_index(:friendships, [:friend_user_id, :user_id])
      remove_index(:friendships, [:user_id, :friend_user_id])
      drop_table :friendships
  end
end

I'm not certain whether there is a shortcut way of creating this table, but bare minimum you can simply do rails g migration create_friendships, and fill in the self.up and self.down methods.

我不确定是否有创建此表的快捷方式，但最低限度你可以简单地执行rails g migration create_friendships，并填写self.up和self.down方法。

And then finally in your user model, you simply add the name of the join table, like so:

最后在您的用户模型中，您只需添加连接表的名称，如下所示：

class User < ActiveRecord::Base
  has_and_belongs_to_many :friends, 
              class_name: "User", 
              join_table: :friendships, 
              foreign_key: :user_id, 
              association_foreign_key: :friend_user_id
end

As you can see, while you do have a join table in the database, there is no related join model.

如您所见，虽然数据库中有连接表，但没有相关的连接模型。

Please let me know whether this works for you.

请告诉我这是否适合您。

#1