如何编写此范围来搜索嵌套模型上的属性?(再次) [英] How do I write this scope to search for attributes on a nested model? (again)

问题描述

好的，

我今天早些时候问过这个问题

I asked this question earlier today

如何编写范围来搜索嵌套模型上的属性?

并在 Rails 中搜索嵌套模型中的属性时得到了很好的答案.

and got a great answer on searching for attributes in nested models in Rails.

在上一个问题中，编写了一个范围来查找所有出院时间为 nil 的入院患者(感谢 tjwallace).

In the previous question a scope was written that found all patients that had an admission with a discharge_time of nil (Thanks tjwallace).

class Patient < ActiveRecord::Base
  has_many :admissions

  scope :admitted, includes(:admissions).where('admissions.discharge_time' => nil)
end

我现在要做的是编写一个名为 :discharged 的​​范围，该范围将进行搜索，返回所有至少有一次入院且出院时间不为零的患者.我试过以下;

What I'm trying to do now is to write a scope called :discharged, that will do a search that returns all patients that have at least one admission with a discharge_time that is not nil. I've tried the following;

scope :discharged, includes(:admissions).where('admissions.discharge_time <> ?', nil)

但这不会返回任何结果(并且数据库中肯定有应该通过正确编写的搜索找到的患者).任何帮助将不胜感激.

but this returns no results (and there are definitely patients in the database that should be found by a correctly written search). Any help will be greatly appreciated.

推荐答案

这是因为在 SQL 中你不能真正将任何东西与 NULL 进行比较，你需要这样写:

This is because in SQL you can't really compare anything to NULL, you need to write something like this:

 scope :discharged, includes(:admissions).where('admissions.discharge_time is not ?', nil)

这是对这种 SQL 行为的一个很好的解释:http://www.xaprb.com/blog/2006/05/18/why-null-never-compares-false-to-anything-in-sql/

Here is a nice explanation of this SQL behavior: http://www.xaprb.com/blog/2006/05/18/why-null-never-compares-false-to-anything-in-sql/

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