渴望在子类上加载关联 [英] eager loading association on a subclass

问题描述

我具有以下（简化的）类层次结构：

I have the following (simplified) class hierarchy:

def Parent < ActiveRecord::Base end
def Child < Parent
  belongs_to :other
end
def Other < ActiveRecord::Base end

我想获取所有Parent对象，如果它们是Child对象，则具有他们渴望加载：other关联。所以我希望我能做到：

I want to get all Parent objects and -if they are Child objects- have them eager load the :other association. So I had hoped I could do:

Parent.find(:all, :include => [:other])

但正如我担心的那样，我得到的信息是：找不到名为 other的协会；也许您拼写错误了吗？

But as I feared, I get the message: "Association named 'other' was not found; perhaps you misspelled it?"

在这种情况下建立紧急加载的最佳方法是什么？

What is the best way to establish eager loading in this scenario?

根据要求，下面是更具体的示例：

As requested, here's the more concrete example:

• 父母=事件


• 儿童= PostEvent


• 其他= Post

我想记录不同类型的事件，所有事件它们自己的属性（其中一些是对其他对象的引用），例如上面的示例。同时，我希望能够列出所有发生的事件，因此列出父类。

I want to log different types of events, all with their own properties (some of which are references to other objects), like the above example. At the same time I want to be able to list all Events that occurred, hence the parent class.

推荐答案

您可以定义 Parent 模型中的 belongs_to：other 关联？它与每个 Parent 对象都不相关，但这就是STI的本质：您几乎总是拥有 some 列，而每个列都不使用

Can you define the belongs_to :other association in the Parent model? It won't be relevant to every Parent object, but that's the nature of STI: you will almost always have some column that's not used by every child.

如果您真的不能将关联移至父级，则可能需要分两个步骤进行加载，例如：

If you really can't move the association to the parent, you may have to load in two steps, for example:

Parent.find(:all, :conditions => "type != 'Child'") +
  Child.find(:all, :include => [:other])

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