Ruby on Rails：has_many 引用——它拥有哪些模型对象？
我是 Rails 新手，已完成 Michael Hartl 的“Ruby on Rails 3 教程”。虽然这本书教了我很多，但我发现这个谜题我不明白。
要预览这个难题，也就是说，我不明白，在 User 模型内部，
has_many :following, :through=>:relationship, :source=>:followed
这段代码如何将“user.following”链接到 User 实例数组。
下面是整个谜题。
首先，我有 Relationship 模型，它记录 followed_id 和 follower_id 信息。在Relationship模型中，关联很简单
class Relationship < ActiveRecord::Base
attr_accessible :followed_id
belongs_to :follower, :class_name => "User"
belongs_to :followed, :class_name => "User"
end
，如下> 关系表中的行通过关系关联。
class User < ActiveRecord::Base
.
.
.
has_many :relationships, :foreign_key => "follower_id", :dependent => :destroy
.
直到现在，我明白了。
但下一行出现了混乱，通过 user.following 它可以组装该用户的所有关注者（用户实例）。像这样，
has_many :following, :through=>:relationships, :source=>:followed
我知道 :source=>:followed 将覆盖默认值，并让查找与该用户关联的所有 followed_ids 。
但是，Rails 如何识别 followed_id 链接到 User 对象？标签名称与 users 不匹配，也未指定 :class_name。我只是不明白 Rails 如何完成这项基础工作，或者我错过了一些提示。
谢谢你！ :)
I am new to Rails and finished Michael Hartl's "Ruby on Rails 3 Tutorial". Although the book teaches me a lot, I find this puzzle I don't understand.
To preview the puzzle, that is, I don't understand, inside User model,
has_many :following, :through=>:relationship, :source=>:followed
how this piece of code link "user.following" to an array of User instances.
And below is the whole puzzle.
First of all, I have the Relationship model, which records followed_id and follower_id infos. Inside Relationship model, the association is simple as
class Relationship < ActiveRecord::Base
attr_accessible :followed_id
belongs_to :follower, :class_name => "User"
belongs_to :followed, :class_name => "User"
end
Then, inside the User model, a user will assume the role of follower, and collect all its following rows in relationships table through relationships association.
class User < ActiveRecord::Base
.
.
.
has_many :relationships, :foreign_key => "follower_id", :dependent => :destroy
.
Until now, I got it.
But confusion came at the next line, where through user.following it can assemble all that user's following(User instances). Like so,
has_many :following, :through=>:relationships, :source=>:followed
I understand that :source=>:followed will overwrite the default, and let find all followed_ids associated with that user.
But, how can Rails recognize followed_id to link to User object? The label name doesn't match users, nor is there :class_name specified. I just don't get how Rails do this underlying work, or I missed out some hints.
Thank you! :)
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Rails 识别出这是一个用户对象，因为它是在Relationship 的belongs_to 中设置的。 Rails 在这里所做的是通过外键“follower_id”跟踪关系类，并返回与当前用户有关系的每个用户，如下所示。当然，Rails 在单个 SQL 语句中执行此操作，如下所示：
Rails recognize that is an user object because it is set in Relationship's belongs_to. What Rails does here is to follow the relationship class through the foreign key "follower_id" and returning every User that has a relationship with the current user as followed. Of course Rails do that in a single SQL statement like this:
这向 Rails 解释说，
following是following的逆关系，并且用户通过他的关系有很多关注和关注。Rails 知道
followed_id链接到 User 的方式是它是在您的Relationship模型中定义的。希望你已经理解了！祝你好运 ：）
This explains to Rails that
followingis the inverse relationship offollowingand that users has many following and followed through his relationships.The way Rails knows that
followed_idis linked to User is that it is defined in yourRelationshipmodel.Hope you've understood ! Good luck :)