Rails includes cache not being used in model method - ruby-on-rails

Question

So in a rails-api I'm working on, we're currently trying to optimize some of the longer running calls, and I'm having an issue with the .includes functionality. I've got it working in most situations, but there's one particular situation where it's not working in the way that I want it to.
Here's an example:
User class
class User < ActiveRecord::Base
has_many :images
has_one :active_image, -> { where(images: { active_image: true })}, class_name: 'Image'
has_many :facebook_auth
def get_profile_image
if active_image
active_image.image.url(:profile)
else
facebook = facebook_auth.last
if facebook
"https://graph.facebook.com/#{facebook.provider_user_id}/picture?width=150&height=150"
end
end
nil
end
end
Controller:
class UserController < BaseAPIController
def get_user_image
user_id = params[:user_id]
user = User.includes(:active_image, :facebook_auth).find(user_id)
render json: user.get_profile_image
end
end
With this, I would assume that the .includes(:active_image, :facebook_auth) would cache the data so that when I call them in the get_profile_image method, it doesn't make any more db calls, but this isn't the case. What am I doing wrong here?
Thanks,
Charlie

Answer 1

You where almost there!
Try this approach:
class User < ApplicationRecord
has_many :images, dependent: :destroy
has_one :active_image,
-> { where(active: true) },
class_name: 'Image'
has_many :facebook_auths, dependent: :destroy
has_one :active_facebook_auth,
-> { order("created_at desc") },
class_name: 'FacebookAuth'
scope :eager_load_image_data,
-> { includes(:active_image).includes(:active_facebook_auth) }
def profile_image_url
if active_image
active_image.url
elsif active_facebook_auth
"https://graph.facebook.com/#{active_facebook_auth.provider_user_id}/picture?width=150&height=150"
else
nil
end
end
end
Then in your controller or whenever you want to eager load images:
# for one user, with id 2:
User.eager_load_image_data.find(2).profile_image_url
# for a collection (using 'all' here):
User.eager_load_image_data.all.map{ |user|
[user.name, user.profile_image_url]
}
This way the image data is eagerloaded, both from the Image class and the FacebookAuth class.
There where also some other issues in your method User#get_profile_image that I have fixed:
It always returns nil. I am sure in your real code you have early returns.
For collections, it does a N+1 query if looking for facebook_auth_tokens.

Answer 2

Well, I wanted to comment, but couldn't put code into the comments, so I'm giving a non-answer...
I don't see anything obviously wrong, but as a work around, you could do this in User or somewhere:
def self.user_profile_image(user_id)
active_image = Images.where(user_id: user_id).where(active_image: true).first
if active_image
active_image.image.url(:profile)
else
facebook = FaceBookAuth.where(user_id: user_id).last
if facebook
"https://graph.facebook.com/#{facebook.provider_user_id}/picture?width=150&height=150"
end
end
nil
end
And just call/cache the image in your controller, if that's not overly simplistic...
def get_user_image
render json: User.user_profile_image(params[:user_id])
end
That makes at most 2 relatively efficient queries. It doesn't needlessly load user, etc.