对范围中的查询使用OR [英] Using OR with queries in a scope

问题描述

在Rails3中，我有：

In Rails3 I have:

Class Teacher
  #  active                 :boolean
  has_and_belongs_to_many :subjects

Class Subject
  #  active                 :boolean
  has_and_belongs_to_many :teachers

我正在尝试构造一个教师范围，该范围返回所有活动或与主题是有效的 。

I am trying to construct a Teacher scope that returns all Teachers that are active or are associated with a Subject that is active.

这些作用域分别起作用，但是如何将它们作为单个范围与OR组合？

These scopes work individually, but how to combine them as a single scope with an OR?

scope :active_teachers, where(active: true)
scope :more_active_teachers, joins(:subjects).where(:subjects => {active: true})

我已经尝试过但没有成功：

I've tried this without success:

scope :active_teachers, where(active: true).or(joins(:subjects)
      .where(:subjects => {active: true}))

UPDAT E：

我以为我有一个解决方案，但这不再是延迟加载，它两次访问数据库，最重要的是，返回一个数组而不是一个

I thought I had a solution, but this no longer lazy loads, hits the database twice and — most importantly — returns an array rather than an AR object!

scope :active_teachers, where(active: true) |
                        joins(:subjects).where(:subjects => {active: true})

推荐答案

您有 Squeel 可以解救。更多详细信息此处。

You have Squeel to your rescue. More details here.

使用该，您可以定义以下内容：

Using that, you could define something like:

class Teacher
  ...
  scope :active_teachers, joins{subjects}.where {(active == true) | (subjects.active == true)}
  ...
end

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