导轨找到相关零的has_many记录记录 [英] Rails find record with zero has_many records associated
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问题描述
这看起来很简单,但我不能让它转起来的谷歌。
如果我有:
类城市与LT;的ActiveRecord :: Base的
的has_many:照片
结束
类图片<的ActiveRecord :: Base的
belongs_to的:城市
结束
我想找到一些没有照片的所有城市。我很想能够调用类似...
City.where(photos.empty?)
...但是,这并不存在。那么,你怎么做这种类型的查询?
更新: 现在已经找到了答案,原来的问题,我很好奇,你是怎么构建逆?
IE浏览器:如果我想创建这些作为的范围:
范围:without_photos,包括(:照片)。凡(:照片=> {:city_id =>无})
适用范围:with_photos,???
解决方案
呸,发现在这里: http://stackoverflow.com /一/四十一万七千八百七十二分之五百五十七万○二百二十一
City.includes(:照片)。凡(照片:{city_id:无})
This seems fairly simple but I can't get it to turn up on Google.
If I have:
class City < ActiveRecord::Base
has_many :photos
end
class Photo < ActiveRecord::Base
belongs_to :city
end
I want to find all cities that have no photos. I'd love to be able to call something like...
City.where( photos.empty? )
...but that doesn't exist. So, how do you do this kind of query?
Update: Having now found an answer to the original question, I'm curious, how do you construct the inverse?
IE: if I wanted to create these as scopes:
scope :without_photos, includes(:photos).where( :photos => {:city_id=>nil} )
scope :with_photos, ???
解决方案
Bah, found it here: http://stackoverflow.com/a/5570221/417872
City.includes(:photos).where(photos: { city_id: nil })
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