How to deal with eval nil issues in Rails - ruby-on-rails

Question

I am facing a pretty nasty error in a production environment that caused a bit of confusion. I increased logging on production to narrow down the issue and was now able to reproduce it on our local environment. So setup wises we are running on Rails 5, on a Ubuntu machine. The application uses ElasticSearch 5.4, and we are storing images on Amazon S3.
Process: A user can upload images. There is a User Index in Elasticsearch that also stores information to the related Photo model.
The issue is that once a user uploads a photo, it sometimes comes to an error on an index page or detailed user page where photos are in one way or another accessed. And the results to be displayed are not read from a database but Elasticsearch.
Workaround (which isn't one). Once the index is getting reimported the error doesn't occur any longer - which initially led me to believe that it has something to do with ElasticSearch.
User Model
class User < ApplicationRecord
include UserSearchable
extend FriendlyId
require "redis"
friendly_id :slug_candidates, use: :slugged
has_many :photos
after_update { self.photos.each(&:touch) }
...
end
User Searchable Concern
module UserSearchable
extend ActiveSupport::Concern
included do
include Elasticsearch::Model
include Elasticsearch::Model::Callbacks
index_name Rails.application.class.parent_name.underscore
document_type self.name.downcase
settings index: { number_of_shards: 1 } do
mapping dynamic: false do
indexes :description, analyzer: 'english'
indexes :tagline, analyzer: 'english'
indexes :username
...
end
end
after_touch() { __elasticsearch__.index_document }
def as_indexed_json(_options = {})
self.as_json(
except: [:email, :lat, :lng, :status, :termsofuse, :v_code],
include: {
photos: { only: [:name, :caption, :active, :image_data, :downloadable, :uploader_id, :public] },
).merge(
location: {lat: lat.to_f, lon: lng.to_f},
age: birthday.nil? ? 18 : ((Date.today - birthday.to_date) / 365.25).floor
)
end
def home_search(searcher, order = nil, how_many = nil)
how_many = 400 unless how_many.is_a?(Integer)
order = 1 unless order.is_a?(Integer)
if self.radius < 30
use_radius = 30
else
use_radius = self.radius
end
search_definition = Jbuilder.encode do |json|
json.sort do
if order == 1
json.array! [{'_geo_distance' => { :location => {:lat => lat, :lon => lng} }}, '_score']
else
json.array! ['_score', {'_geo_distance' => { :location => {:lat => lat, :lon => lng} }}]
end
end
json.query do
json.bool do
json.filter do
json.bool do
json.must do
json.array! [:geo_distance => { :distance => use_radius, :unit => "mi", :location => {:lat => self.lat, :lon => self.lng}, :boost => 5.0}]
end
...
unless searcher.id.nil?
json.must_not do
json.array! [ {:term => { 'id' => self.id }} ]
end
end
end
end
...
end
end
# json.size how_many
end
self.class.__elasticsearch__.search(search_definition)
end
end
end
Photo Model
class Photo < ApplicationRecord
include ImageUploader[:image]
include ActiveModel::Validations
acts_as_taggable
before_create :set_name
belongs_to :user, touch: true
after_update { self.user(&:touch) }
private
def set_name
self.name = "Photo"
end
end
Tests of issue in console:
Here, and this is key to the problem. If I eval for the photo sometimes it is nil, and sometimes it is not! And I cannot figure out why? If I run this command lets say 10 times on console, it is nil 2 out of 10 times. And that is when the production system is thrown off its track and the user is presented with an error. As the system is intranet and new we actually show exceptions to users (so do not be alarmed by bad exception handling - users don't say a thing if you don't make it clear ;) )
>> eval(user.photos.sample.image_data)[:small][:id]
=> "photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg"
>> eval(user.photos.sample.image_data)[:small][:id]
!! #<NoMethodError: undefined method `[]' for nil:NilClass>
Additional trace:
>> Settings.s3 + eval(user.photos.sample.image_data)[:small][:id]
!! #<NoMethodError: undefined method `[]' for nil:NilClass>
>> eval(user.photos.sample.image_data)[:small][:id]
=> "photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg"
>> eval(user.photos.sample.image_data)[:small][:id]
=> "photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg"
>> eval(user.photos.sample.image_data)[:small][:id]
=> "photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg"
>> eval(user.photos.sample.image_data)[:small][:id]
=> "photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg"
>> eval(user.photos.sample.image_data)[:small][:id]
!! #<NoMethodError: undefined method `[]' for nil:NilClass>
>> eval(user.photos.sample.image_data)[:small][:id]
=> "photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg"
>> eval(user.photos.sample.image_data)[:small][:id]
!! #<NoMethodError: undefined method `[]' for nil:NilClass>
>> eval(user.photos.sample.image_data)[:small][:id]
!! #<NoMethodError: undefined method `[]' for nil:NilClass>
>> eval(user.photos.sample.image_data)[:small][:id]
=> "photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg"
>>
=> nil
>> eval(user.photos.sample.image_data)[:small][:id]
=> "photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg"
>> eval(user.photos.sample.image_data)[:small][:id]
=> "photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg"
>> eval(user.photos.sample.image_data)[:small][:id]
=> "photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg"
>> eval(user.photos.sample.image_data)[:small][:id]
!! #<NoMethodError: undefined method `[]' for nil:NilClass>
>> user.photos.sample.image_data
=> "{\"original\":{\"id\":\"photo/47/image/original-114c9db755b25afe0398f5b25aed5bef.jpg\",\"storage\":\"store\",\"metadata\":{\"size\":61357,\"filename\":\"London-Escort-Angelina (5).jpg\",\"mime_type\":\"image/jpeg\",\"width\":500,\"height\":500}},\"large\":{\"id\":\"photo/47/image/large-c3985d412ee05495594caa659feca371.jpg\",\"storage\":\"store\",\"metadata\":{\"filename\":\"shrine-s320170627-29702-17km6c5.jpg\",\"size\":61356,\"mime_type\":\"image/jpeg\",\"width\":500,\"height\":500}},\"small\":{\"id\":\"photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg\",\"storage\":\"store\",\"metadata\":{\"filename\":\"shrine-s320170627-29702-ouo63f.jpg\",\"size\":25642,\"mime_type\":\"image/jpeg\",\"width\":300,\"height\":300}}}"
>> user.photos.sample.image_data[:small]
!! #<TypeError: no implicit conversion of Symbol into Integer>
>> eval(user.photos.sample.image_data)[:small]
=> {:id=>"photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg", :storage=>"store", :metadata=>{:filename=>"shrine-s320170627-29702-ouo63f.jpg", :size=>25642, :mime_type=>"image/jpeg", :width=>300, :height=>300}}
>> eval(user.photos.sample.image_data)[:small][:id]
=> "photo/47/image/small-2cd0928d02826f0614086a01ee97ef32.jpg"
>> eval(user.photos.sample.image_data)[:small][:id]
!! #<NoMethodError: undefined method `[]' for nil:NilClass>
Any help is much appreciated!!!

Answer 1

Your results are different because you use sample method, whitch choose a random element from user.photos.
For prevent undefined method [] for nil:NilClass error you can use &.dig for ruby >= 2.3 or try if less
nil&.dig(:small, :id)
=> nil
nil.try(:dig, :small, :id)
=> nil

Answer 2

So, I could resolve the issue (workaround-ish) by reindexing the updated user document when a photo is uploaded or deleted. Forgot about the destroy part before. It doesn't seem right as it is messy given an entire record must be removed in ES and reindexed, but traffic is low and for the time being it works. If I figure out the issue, I will revert to this thread.