ActiveRecord的，双belongs_to的

问题描述：

我有2个型号：链接和用户如：

class Link < ActiveRecord::Base
  belongs_to :src_user
  belongs_to :dst_user
end

class User < ActiveRecord::Base
  has_many :links
end

一个模式可能看起来像：

A schema could looking like:

+----------+     +------+
| Link     |     | User |
+----------+     |------+
| src_user |---->|      |
| dst_user |---->|      |
+----------+     +------+

我的问题是：我怎么能修改用户模型做才能做到这一点的

My question is: how can I edit User model do in order to do this

@user.links # => [list of links]

（...这应该查询@ user.src_users + @ users.dst_users，具有唯一性如果可能的话。）

(...which should query @user.src_users + @users.dst_users, with unicity if possible.)

我们能做到这一点只使用SQL中的ActiveRecord？非常感谢。

Can we do this only using SQL inside ActiveRecord? Many thanks.

（注意：我on Rails的3.1.1）

(note: I'm on Rails 3.1.1)

答

您必须指定用户模型中多关系，所以它知道哪些特定的关联，将附加到。

You have to specify multiple relations inside the user model so it knows which specific association it will attach to.

class Link < ActiveRecord::Base
  belongs_to :src_user, class_name: 'User'
  belongs_to :dst_user, class_name: 'User'
end

class User < ActiveRecord::Base
  has_many :src_links, class_name: 'Link', inverse_of: :src_user
  has_many :dst_links, class_name: 'Link', inverse_of: :dst_user
end

的：必须指定选项将class_name因为该协会的名称并不是简单：链接。您可能还需要指定：inverse_of在链接模式的选择，但我不能肯定这一点。如果你没有它不会伤害，但。

The :class_name option must be specified since the association name is not simply :links. You may also need to specify the :inverse_of option in the Link model, but I can't be sure of that. It wouldn't hurt if you did, though.

为了做你的@ user.links电话，你就必须做这样的事情：

In order to do your @user.links call, you'll have to do something like this:

class User < ActiveRecord::Base
  def links
    Link.where(['src_user = ? OR dst_user = ?', self.id, self.id])
  end
end

...因为ActiveRecord的不提供一种方式来合并在同一个模型两个关联为一个。

… since ActiveRecord doesn't provide a way to merge two associations on the same model into one.

ActiveRecord的，双belongs_to的

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