Rails 查找具有零个 has_many 记录的记录 [英] Rails find record with zero has_many records associated

问题描述

这看起来很简单，但我无法在 Google 上显示.

This seems fairly simple but I can't get it to turn up on Google.

如果我有:

class City < ActiveRecord::Base
  has_many :photos
end

class Photo < ActiveRecord::Base
  belongs_to :city
end

我想找到所有没有照片的城市.我希望能够调用类似...

I want to find all cities that have no photos. I'd love to be able to call something like...

City.where( photos.empty? )

...但这并不存在.那么，您如何进行此类查询?

...but that doesn't exist. So, how do you do this kind of query?

更新:现在找到了原始问题的答案，我很好奇，你如何构造逆?

Update: Having now found an answer to the original question, I'm curious, how do you construct the inverse?

IE:如果我想将这些创建为范围:

IE: if I wanted to create these as scopes:

scope :without_photos, includes(:photos).where( :photos => {:city_id=>nil} )
scope :with_photos, ???

推荐答案

呸，在这里找到:https://stackoverflow.com/a/5570221/417872

City.includes(:photos).where(photos: { city_id: nil })

这篇关于Rails 查找具有零个 has_many 记录的记录的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！