CODEWITHSUNDEEP
activerecord
Nathan Long
Nathan Long

Reputation: 125902

ActiveRecord: check whether association exists without loading it?

Suppose I've got ActiveRecord models such that User has_one :photo. In the database, photos has a t.binary column which may hold a lot of data, so I don't want to SELECT that column unless I need to.

I want to do something like:

users.each do |user|
  image_tag(user_photo_path) if user.photo.present?
end

However, I don't want to call user.photo.present? because:

What I really want is to load users with a single query which gives each one a property telling me whether it has an associated photo or not.

Upvotes: 2

Views: 193

Answers (1)

Nathan Long
Nathan Long

Reputation: 125902

With ActiveRecord 5, this works:

class User < ActiveRecord::Base                                                                                                                                     
  scope :with_photo_id, -> { 
     left_outer_joins(:photo).select(
       "users.*, photos.id AS photo_id"
     )
   }

 end

Then I can call User.with_photo_id and check user.photo_id.present?.

Prior to AR 5, the join would be uglier:

  joins(
    "LEFT OUTER JOIN photos ON photos.user_id = users.id"
  )

Upvotes: 1

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