ActiveRecord的，的has_many：通过和多态关联 [英] ActiveRecord, has_many :through, and Polymorphic Associations

问题描述

伙计们，

想确保我正确地理解这一点。并请忽略继承的情况下在这里（SentientBeing），试图转而专注于多态模型的has_many：通过关系。尽管如此，考虑以下...

Want to make sure I understand this correctly. And please disregard the case for inheritance here (SentientBeing), trying to instead focus on polymorphic models in has_many :through relationships. That said, consider the following...

class Widget < ActiveRecord::Base
  has_many :widget_groupings

  has_many :people, :through => :widget_groupings, :source => :person, :conditions => "widget_groupings.grouper_type = 'Person'"
  has_many :aliens, :through => :widget_groupings, :source => :alien, :conditions => "video_groupings.grouper_type = 'Alien'"
end

class Person < ActiveRecord::Base
  has_many :widget_groupings, :as => grouper
  has_many :widgets, :through => :widget_groupings
end

class Alien < ActiveRecord::Base
  has_many :widget_groupings, :as => grouper
  has_many :widgets, :through => :widget_groupings  
end

class WidgetGrouping < ActiveRecord::Base
  belongs_to :widget
  belongs_to :grouper, :polymorphic => true
end

在一个完美的世界，我想，给一个Widget和一个人，做这样的事情：

In a perfect world, I'd like to, given a Widget and a Person, do something like:

widget.people << my_person

然而，当我做到这一点，我已经注意到了'斑'的'型'总是在widget_groupings空。不过，如果我到类似如下：

However, when I do this, I've noticed the 'type' of the 'grouper' is always null in widget_groupings. However, if I to something like the following:

widget.widget_groupings << WidgetGrouping.new({:widget => self, :person => my_person})

然后，所有的作品，因为我本来正常的预期。我不认为我见过这种情况发生非多态关联，只是想知道这是否是一些具体的事情到这个用例，或者我可能会盯着一个错误。

Then all works as I would have normally expected. I don't think I've ever seen this occur with non polymorphic associations and just wanted to know if this was something specific to this use case or if I'm potentially staring at a bug.

感谢您的帮助！

推荐答案

有一个已知问题使用Rails 3.1.1，打破了这个功能。如果你有这个问题的第一次尝试升级，它被固定在3.1.2

There is a known issue with Rails 3.1.1 that breaks this functionality. If you are having this problem first try upgrading, it's been fixed in 3.1.2

您是如此接近。问题是你滥用：源选项。 ：源应指向多态性belongs_to的关系。然后，所有你需要做的就是指定：SOURCE_TYPE为你想定义的关系

You're so close. The problem is you're misusing the :source option. :source should points to the polymorphic belongs_to relationship. Then all you need to do is specify :source_type for the relationship you're trying to define.

此修复程序的窗口小部件模型应该让你做你正在寻找什么。

This fix to the Widget model should allow you do exactly what you're looking for.

class Widget < ActiveRecord::Base
  has_many :widget_groupings

  has_many :people, :through => :widget_groupings, :source => :grouper, :source_type => 'Person'
  has_many :aliens, :through => :widget_groupings, :source => :grouper, :source_type => 'Alien'
end

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