Caching sum privileged reaction scores (#15299)

* Caching sum privileged reaction scores

This relates to work on improving the feed.  Namely that in the current
proposal in PR #15240 I'm not accounting for how privileged users have
given feedback on an article.

With this change, I will now have a cached value on the articles table
that can be a proxy for how the privileged users have reacted.

In addition there's a small refactor that moves a constant to the
correct scoping object.

Dependent on #15283.

* Fixing method name to `exists?`

Prior to this commit, I was using `exist?` which doesn't work for
ActiveRecord::Relation objects.

app/controllers/admin/privileged_reactions_controller.rb

@@ -2,12 +2,10 @@ module Admin
   class PrivilegedReactionsController < Admin::ApplicationController
     layout "admin"
 
-    PRIVILEGED_REACTION_CATEGORIES = %i[thumbsup thumbsdown vomit].freeze
-
     def index
       @q = Reaction
         .includes(:user, :reactable)
-        .where(category: PRIVILEGED_REACTION_CATEGORIES)
+        .privileged_category
         .order(created_at: :desc)
         .ransack(params[:q])
       @privileged_reactions = @q.result.page(params[:page] || 1).per(25)

app/models/article.rb

@@ -460,6 +460,7 @@ class Article < ApplicationRecord
   def update_score
     self.score = reactions.sum(:points) + Reaction.where(reactable_id: user_id, reactable_type: "User").sum(:points)
     update_columns(score: score,
+                   privileged_users_reaction_points_sum: reactions.privileged_category.sum(:points),
                    comment_score: comments.sum(:score),
                    hotness_score: BlackBox.article_hotness_score(self),
                    spaminess_rating: BlackBox.calculate_spaminess(self))

app/models/reaction.rb

@@ -5,8 +5,14 @@ class Reaction < ApplicationRecord
     "thumbsdown" => -10.0
   }.freeze
 
+  # The union of public and privileged categories
   CATEGORIES = %w[like readinglist unicorn thinking hands thumbsup thumbsdown vomit].freeze
+
+  # These are the general category of reactions that anyone can choose
   PUBLIC_CATEGORIES = %w[like readinglist unicorn thinking hands].freeze
+
+  # These are categories of reactions that administrators can select
+  PRIVILEGED_CATEGORIES = %w[thumbsup thumbsdown vomit].freeze
   REACTABLE_TYPES = %w[Comment Article User].freeze
   STATUSES = %w[valid invalid confirmed archived].freeze
 
@@ -31,6 +37,7 @@ class Reaction < ApplicationRecord
       .or(comment_vomits.where(reactable_id: user.comment_ids))
       .or(user_vomits.where(user_id: user.id))
   }
+  scope :privileged_category, -> { where(category: PRIVILEGED_CATEGORIES) }
 
   validates :category, inclusion: { in: CATEGORIES }
   validates :reactable_type, inclusion: { in: REACTABLE_TYPES }

lib/data_update_scripts/20211104200856_update_each_articles_privileged_user_point_count.rb

@@ -0,0 +1,17 @@
+module DataUpdateScripts
+  class UpdateEachArticlesPrivilegedUserPointCount
+    def run
+      # This code is "idempotent" in that it's calculating and caching a value stored elsewhere.
+      Article.find_in_batches do |articles|
+        articles.each do |article|
+          # Given that we have a default of 0, don't update if we
+          # don't have any reactions.
+          next unless article.reactions.privileged_category.exists?
+
+          article.update_column(:privileged_users_reaction_points_sum,
+                                article.reactions.privileged_category.sum(:points))
+        end
+      end
+    end
+  end
+end

spec/lib/data_update_scripts/update_each_articles_privileged_user_point_count_spec.rb

@@ -0,0 +1,17 @@
+require "rails_helper"
+require Rails.root.join(
+  "lib/data_update_scripts/20211104200856_update_each_articles_privileged_user_point_count.rb",
+)
+
+describe DataUpdateScripts::UpdateEachArticlesPrivilegedUserPointCount do
+  it "updates articles scores" do
+    article = create(:article)
+    user = create(:user, :trusted)
+    reaction = create(:thumbsdown_reaction, user: user, reactable: article)
+
+    # Short-circuiting callbacks
+    reaction.update_column(:points, 1_000_000)
+
+    expect { described_class.new.run }.to change { article.reload.privileged_users_reaction_points_sum }.to(1_000_000)
+  end
+end

spec/models/article_spec.rb

@@ -1331,6 +1331,14 @@ RSpec.describe Article, type: :model do
       article.update_score
       expect { article.update_score }.not_to change { article.reload.hotness_score }
     end
+
+    it "caches the privileged score values" do
+      user = create(:user, :trusted)
+
+      create(:thumbsdown_reaction, reactable: article, user: user)
+
+      expect { article.update_score }.to change { article.reload.privileged_users_reaction_points_sum }
+    end
   end
 
   describe "#feed_source_url and canonical_url must be unique for published articles" do